Add gitter for community.

README.md

@@ -1,4 +1,6 @@
 ## ![Papers We Love](http://paperswelove.org/images/logo-top.svg)
+ 
+ [![Gitter](https://badges.gitter.im/papers-we-love/community.svg)](https://gitter.im/papers-we-love/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 
 **Papers We Love** (*PWL*) is a community built around reading, discussing and learning more about academic computer science papers. This repository serves as a directory of some of the best papers the community can find, bringing together documents scattered across the web. You can also visit the [Papers We Love site](http://paperswelove.org/) for more info.