Add gitter.im badge (#427)

Author: ddemidov

README.rst

@@ -6,6 +6,9 @@ Python language bindings for ev3dev
 .. image:: https://readthedocs.org/projects/python-ev3dev/badge/?version=stable
     :target: http://python-ev3dev.readthedocs.org/en/stable/?badge=stable
     :alt: Documentation Status
+.. image:: https://badges.gitter.im/ev3dev/chat.svg
+    :target: https://gitter.im/ev3dev/chat
+    :alt: Chat at https://gitter.im/ev3dev/chat
 
 A Python3 library implementing an interface for ev3dev_ devices,
 letting you control motors, sensors, hardware buttons, LCD