Update README.md

Author: CXuesong

README.md

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 # LanguageServer.NET
 
-A .NET implementation of [Language Server Protocol](https://github.com/Microsoft/language-server-protocol/blob/master/protocol.md) infrastructure library for VSCode, and hopefully, might also be used with other IDEs that support Language Server Protocol. Still work in progress and API is subject to change.
+[![Gitter](https://badges.gitter.im/CXuesong/LanguageServer.NET.svg?style=flat-square)](https://gitter.im/CXuesong/LanguageServer.NET?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+
+A .NET implementation of [Language Server Protocol](https://github.com/Microsoft/language-server-protocol/blob/master/protocol.md) infrastructure library for VSCode, and hopefully, might also be used with other IDEs that support Language Server Protocol. It supports LSP 2.0 and should support LSP 3.x (if not, please open an issue; thanks).
 
 ![Screenshot of DemoLanguageServer](README.resource/Screenshot.gif)