Merge pull request #1135 from gitter-badger/gitter-badge

Add a Gitter chat badge to README.md

README.md

 # QGroundControl
 ## Open Source Micro Air Vehicle Ground Control Station
 
+[![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/mavlink/qgroundcontrol?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
 
 * Project:
 <http://qgroundcontrol.org>