update docs with grpc-dotnet info

README.md

@@ -72,7 +72,7 @@ Libraries in different languages may be in various states of development. We are
 | Ruby                    | [src/ruby](src/ruby)                |
 | Python                  | [src/python](src/python)            |
 | PHP                     | [src/php](src/php)                  |
-| C#                      | [src/csharp](src/csharp)            |
+| C# (core library based) | [src/csharp](src/csharp)            |
 | Objective-C             | [src/objective-c](src/objective-c)  |
 
 | Language                | Source repo                                          |
@@ -82,4 +82,4 @@ Libraries in different languages may be in various states of development. We are
 | NodeJS                  | [grpc-node](https://github.com/grpc/grpc-node)       |
 | WebJS                   | [grpc-web](https://github.com/grpc/grpc-web)         |
 | Dart                    | [grpc-dart](https://github.com/grpc/grpc-dart)       |
-
+| .NET (pure C# impl.)    | [grpc-dotnet](https://github.com/grpc/grpc-dotnet)   |