chore: regenerate README

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

2021-03-03 19:44:32,823 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-iamcredentials/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-03-03 19:44:33,688 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

Full log will be available here:
https://source.cloud.google.com/results/invocations/d03a5992-3e0e-4cc1-9a28-06a786482027/targets

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[codecov]

Codecov Report

Merging #376 (9308131) into master (4723c28) will decrease coverage by 0.06%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #376      +/-   ##
============================================
- Coverage     75.14%   75.07%   -0.07%     
+ Complexity       57       48       -9     
============================================
  Files             6        6              
  Lines           350      333      -17     
  Branches          5        5              
============================================
- Hits            263      250      -13     
  Misses           82       82              
+ Partials          5        1       -4     

Impacted Files	Coverage Δ	Complexity Δ
...am/credentials/v1/stub/GrpcIamCredentialsStub.java	90.00% <0.00%> (-0.66%)	10.00% <0.00%> (-1.00%)
...redentials/v1/stub/IamCredentialsStubSettings.java	79.61% <0.00%> (-0.39%)	13.00% <0.00%> (ø%)
...cloud/iam/credentials/v1/IamCredentialsClient.java	81.70% <0.00%> (+2.81%)	19.00% <0.00%> (-8.00%)	⬆️

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[yoshi-approver]

Rubber stamped PR!