Normalize flag description in help command

[tbobm]

Thanks a lot for this wonderful tool 🙇‍♂️

Currently descriptions are a mixin of Capitalized and lowercased with different phrasing styles.

This PR aims to normalize this and set a baseline for future additions by standardizing
every description to match UNIX conventions (lowercase + imperative tone).

~ act --help
Run GitHub actions locally by specifying the event name (e.g. `push`) or an action name directly.

Usage:
  act [event name to run] [flags]

If no event name passed, will default to "on: push"
If actions handles only one event it will be used as default instead of "on: push"

Flags:
      --action-cache-path string                          Defines the path where the actions get cached and host workspaces created. (default "/home/bob/.cache/act")
      --action-offline-mode                               If action contents exists, it will not be fetch and pull again. If turn on this, will turn off force pull
  -a, --actor string                                      user that triggered the event (default "nektos/act")
      --artifact-server-addr string                       Defines the address to which the artifact server binds. (default "172.16.47.105")
      --artifact-server-path string                       Defines the path where the artifact server stores uploads and retrieves downloads from. If not specified the artifact server will not start.
      --artifact-server-port string                       Defines the port where the artifact server listens. (default "34567")
  -b, --bind                                              bind working directory to container, rather than copy
      --bug-report                                        Display system information for bug report
      --cache-server-addr string                          Defines the address to which the cache server binds. (default "172.16.47.105")
      --cache-server-path string                          Defines the path where the cache server stores caches. (default "/home/bob/.cache/actcache")
      --cache-server-port uint16                          Defines the port where the artifact server listens. 0 means a randomly available port.
      --container-architecture string                     Architecture which should be used to run containers, e.g.: linux/amd64. If not specified, will use host default architecture. Requires Docker server API Version 1.41+. Ignored on earlier Docker server platforms.
      --container-cap-add stringArray                     kernel capabilities to add to the workflow containers (e.g. --container-cap-add SYS_PTRACE)
      --container-cap-drop stringArray                    kernel capabilities to remove from the workflow containers (e.g. --container-cap-drop SYS_PTRACE)
      --container-daemon-socket string                    URI to Docker Engine socket (e.g.: unix://~/.docker/run/docker.sock or - to disable bind mounting the socket)
      --container-options string                          Custom docker container options for the job container without an options property in the job definition
      --defaultbranch string                              the name of the main branch
      --detect-event                                      Use first event type from workflow as event that triggered the workflow
  -C, --directory string                                  working directory (default ".")
  -n, --dryrun                                            disable container creation, validates only workflow correctness
      --env stringArray                                   env to make available to actions with optional value (e.g. --env myenv=foo or --env myenv)
      --env-file string                                   environment file to read and use as env in the containers (default ".env")
  -e, --eventpath string                                  path to event JSON file
      --github-instance string                            GitHub instance to use. Only use this when using GitHub Enterprise Server. (default "github.com")
  -g, --graph                                             draw workflows
  -h, --help                                              help for act
      --input stringArray                                 action input to make available to actions (e.g. --input myinput=foo)
      --input-file string                                 input file to read and use as action input (default ".input")
      --insecure-secrets                                  NOT RECOMMENDED! Doesn't hide secrets while printing logs.
  -j, --job string                                        run a specific job ID
      --json                                              Output logs in json format
  -l, --list                                              list workflows
      --list-options                                      Print a json structure of compatible options
      --local-repository stringArray                      Replaces the specified repository and ref with a local folder (e.g. https://github.com/test/test@v0=/home/act/test or test/test@v0=/home/act/test, the latter matches any hosts or protocols)
      --log-prefix-job-id                                 Output the job id within non-json logs instead of the entire name
      --man-page                                          Print a generated manual page to stdout
      --matrix stringArray                                specify which matrix configuration to include (e.g. --matrix java:13
      --network string                                    Sets a docker network name. Defaults to host. (default "host")
      --no-cache-server                                   Disable cache server
      --no-recurse                                        Flag to disable running workflows from subdirectories of specified path in '--workflows'/'-W' flag
      --no-skip-checkout                                  Use actions/checkout instead of copying local files into container
  -P, --platform stringArray                              custom image to use per platform (e.g. -P ubuntu-18.04=nektos/act-environments-ubuntu:18.04)
      --privileged                                        use privileged mode
  -p, --pull                                              pull docker image(s) even if already present (default true)
  -q, --quiet                                             disable logging of output from steps
      --rebuild                                           rebuild local action docker image(s) even if already present (default true)
      --remote-name string                                git remote name that will be used to retrieve url of git repo (default "origin")
      --replace-ghe-action-token-with-github-com string   If you are using replace-ghe-action-with-github-com  and you want to use private actions on GitHub, you have to set personal access token
      --replace-ghe-action-with-github-com stringArray    If you are using GitHub Enterprise Server and allow specified actions from GitHub (github.com), you can set actions on this. (e.g. --replace-ghe-action-with-github-com =github/super-linter)
  -r, --reuse                                             don't remove container(s) on successfully completed workflow(s) to maintain state between runs
      --rm                                                automatically remove container(s)/volume(s) after a workflow(s) failure
  -s, --secret stringArray                                secret to make available to actions with optional value (e.g. -s mysecret=foo or -s mysecret)
      --secret-file string                                file with list of secrets to read from (e.g. --secret-file .secrets) (default ".secrets")
      --use-gitignore                                     Controls whether paths specified in .gitignore should be copied into container (default true)
      --use-new-action-cache                              Enable using the new Action Cache for storing Actions locally
      --userns string                                     user namespace to use
      --var stringArray                                   variable to make available to actions with optional value (e.g. --var myvar=foo or --var myvar)
      --var-file string                                   file with list of vars to read from (e.g. --var-file .vars) (default ".vars")
  -v, --verbose                                           verbose output
      --version                                           version for act
  -w, --watch                                             watch the contents of the local repo and run when files change
  -W, --workflows string                                  path to workflow file(s) (default "./.github/workflows/")

This helper becomes the following:

~ go run main.go --help
Run GitHub actions locally by specifying the event name (e.g. `push`) or an action name directly.

Usage:
  act [event name to run] [flags]

If no event name passed, will default to "on: push"
If actions handles only one event it will be used as default instead of "on: push"

Flags:
      --action-cache-path string                          define the path where the actions get cached and host workspaces created (default "/home/bob/.cache/act")
      --action-offline-mode                               prioritize using locally downloaded action contents when it exists and disable force pull
  -a, --actor string                                      define which user triggered the event (default "nektos/act")
      --artifact-server-addr string                       define the address to which the artifact server binds to (default "172.16.47.105")
      --artifact-server-path string                       define the path where the artifact server stores uploads and retrieves downloads from, required to start the artifact server
      --artifact-server-port string                       define the port where the artifact server listens (default "34567")
  -b, --bind                                              bind working directory to container, rather than copy
      --bug-report                                        display system information for bug report
      --cache-server-addr string                          define the address to which the cache server binds to (default "172.16.47.105")
      --cache-server-external-url string                  set the external URL the cache server if it is behind a proxy (e.g.: https://act-cache-server.example.com, make sure there is no trailing slash)
      --cache-server-path string                          define the path where the cache server stores caches. (default "/home/bob/.cache/actcache")
      --cache-server-port uint16                          define the port where the artifact server listens, 0 will use a randomly available port
      --container-architecture string                     set which architecture should be used to run containers, e.g.: linux/amd64. If not specified, use host default architecture. Requires Docker server API Version 1.41+. Ignored on earlier Docker server platforms.
      --container-cap-add stringArray                     grant kernel capabilities to add to the workflow containers (e.g. --container-cap-add SYS_PTRACE)
      --container-cap-drop stringArray                    grant kernel capabilities to remove from the workflow containers (e.g. --container-cap-drop SYS_PTRACE)
      --container-daemon-socket string                    set the URI to Docker Engine socket (e.g.: unix://~/.docker/run/docker.sock or - to disable bind mounting the socket)
      --container-options string                          add custom docker container options for the job container without an options property in the job definition
      --defaultbranch string                              the name of the main branch
      --detect-event                                      use first event type from workflow as event that triggered the workflow
  -C, --directory string                                  override the working directory (default ".")
  -n, --dryrun                                            disable container creation, only validate workflow correctness
      --env stringArray                                   set env variable(s) to make available to actions with optional value (e.g. --env myenv=foo or --env myenv)
      --env-file string                                   set environment file to read and use as env in the containers (default ".env")
  -e, --eventpath string                                  set the path to event JSON file that will be used as an input for the workflow
      --github-instance string                            set which GitHub instance to use, only use this when using GitHub Enterprise Server (default "github.com")
  -g, --graph                                             draw workflows
  -h, --help                                              help for act
      --input stringArray                                 set action input to make available to actions (e.g. --input myinput=foo)
      --input-file string                                 set input file to read and use as action input (default ".input")
      --insecure-secrets                                  NOT RECOMMENDED: display secrets in logs
  -j, --job string                                        run a specific job ID
      --json                                              switch log format to json
  -l, --list                                              list workflows
      --list-options                                      print a json structure of compatible options
      --local-repository stringArray                      replace the specified repository and ref with a local folder (e.g. https://github.com/test/test@v0=/home/act/test or test/test@v0=/home/act/test, the latter matches any hosts or protocols)
      --log-prefix-job-id                                 output the job id within non-json logs instead of the entire name
      --man-page                                          print a generated manual page to stdout
      --matrix stringArray                                specify which matrix configuration to include (e.g. --matrix java:13
      --network string                                    set a docker network name, defaults to "host" (default "host")
      --no-cache-server                                   disable the cache server
      --no-recurse                                        prevent running workflows from subdirectories of specified path in '--workflows'/'-W' flag
      --no-skip-checkout                                  use actions/checkout instead of copying local files into container
  -P, --platform stringArray                              custom image to use per platform (e.g. -P ubuntu-18.04=nektos/act-environments-ubuntu:18.04)
      --privileged                                        use privileged mode
  -p, --pull                                              pull docker image(s) even if already present (default true)
  -q, --quiet                                             disable logging of output from steps
      --rebuild                                           rebuild local action docker image(s) even if already present (default true)
      --remote-name string                                set the git remote name that will be used to retrieve url of git repo (default "origin")
      --replace-ghe-action-token-with-github-com string   if you are using replace-ghe-action-with-github-com and you want to use private actions on GitHub, you have to set personal access token
      --replace-ghe-action-with-github-com stringArray    if you are using GitHub Enterprise Server and allow specified actions from GitHub (github.com), you can set actions on this (e.g. --replace-ghe-action-with-github-com =github/super-linter)
  -r, --reuse                                             keep container(s) on successfully completed workflow(s) to maintain state between runs
      --rm                                                automatically remove container(s)/volume(s) after a workflow(s) failure
  -s, --secret stringArray                                set secret(s) to make available to actions with optional value (e.g. -s mysecret=foo or -s mysecret)
      --secret-file string                                set a file with list of secrets to read from (e.g. --secret-file .secrets) (default ".secrets")
      --use-gitignore                                     control whether paths specified in .gitignore should be copied into container (default true)
      --use-new-action-cache                              enable using the new Action Cache for storing Actions locally
      --userns string                                     user namespace to use
      --var stringArray                                   set variable(s) to make available to actions with optional value (e.g. --var myvar=foo or --var myvar)
      --var-file string                                   set a file with list of vars to read from (e.g. --var-file .vars) (default ".vars")
  -v, --verbose                                           set output to verbose
      --version                                           version for act
  -w, --watch                                             watch the contents of the local repo and run when files change
  -W, --workflows string                                  set path to workflow file(s) directory (default "./.github/workflows/")