[docs] add gitter chat badge

README.md

@@ -12,7 +12,9 @@ Check out the [project site](http://caffe.berkeleyvision.org) for all the detail
 
 and step-by-step examples.
 
-Please join the [caffe-users group](https://groups.google.com/forum/#!forum/caffe-users) to ask questions and talk about methods and models.
+[![Join the chat at https://gitter.im/BVLC/caffe](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/BVLC/caffe?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
+Please join the [caffe-users group](https://groups.google.com/forum/#!forum/caffe-users) or [gitter chat](https://gitter.im/BVLC/caffe) to ask questions and talk about methods and models.
 Framework development discussions and thorough bug reports are collected on [Issues](https://github.com/BVLC/caffe/issues).
 
 Happy brewing!