add gitter to README

README.md

@@ -5,6 +5,7 @@
 [![devDependency Status](https://img.shields.io/david/dev/DIYgod/dplayer.svg?style=flat-square)](https://david-dm.org/DIYgod/DPlayer#info=devDependencies)
 [![npm](https://img.shields.io/npm/dt/dplayer.svg?style=flat-square)](https://www.npmjs.com/package/dplayer)
 [![Travis](https://img.shields.io/travis/DIYgod/DPlayer.svg?style=flat-square)](https://travis-ci.org/DIYgod/DPlayer)
+[![gitter](https://img.shields.io/gitter/room/DIYgod/DPlayer.svg?style=flat-square)](https://gitter.im/diygod233/dplayer)
 [![%e2%9d%a4](https://img.shields.io/badge/made%20with-%e2%9d%a4-ff69b4.svg?style=flat-square)](https://www.anotherhome.net/)
 
 > Wow, such a lovely HTML5 danmaku video player