Add Discord widget to README (#16)

Author: coadler

README.md

@@ -3,6 +3,7 @@
 [!["Open Issues"](https://img.shields.io/github/issues-raw/codercom/code-server.svg)](https://github.com/codercom/code-server/issues)
 [!["Latest Release"](https://img.shields.io/github/release/codercom/code-server.svg)](https://github.com/codercom/code-server/releases/latest)
 [![MIT license](https://img.shields.io/badge/license-MIT-green.svg)](#)
+[![Discord](https://discordapp.com/api/guilds/463752820026376202/widget.png)](https://discord.gg/zxSwN8Z)
 
 `code-server` is VS Code running on a remote server, accessible through the browser.