Update client-libraries.md

Author: ThomasPe

using-the-rest-api/client-libraries.md

@@ -19,3 +19,6 @@ The [Backbone.js client](https://developer.wordpress.org/rest-api/backbone-javas
 ## Ruby
 
 [wp-api-client](https://github.com/duncanjbrown/wp-api-client): a read-only REST API client written in Ruby.
+
+## C# / .NET
+[WordPressPCL](https://github.com/wp-net/WordPressPCL): a full REST API client written in C#.