Added Gitter badge

README.md

@@ -1,4 +1,5 @@
 # RT-Thread #
+[![Gitter](https://badges.gitter.im/Join Chat.svg)](https://gitter.im/RT-Thread/rt-thread?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
 [![Build Status](https://travis-ci.org/RT-Thread/rt-thread.png)](https://travis-ci.org/RT-Thread/rt-thread)