Added documentation badge from readthedocs.

Author: veeresht

README.rst

@@ -4,9 +4,11 @@
 
 .. |Travis| image:: https://secure.travis-ci.org/veeresht/CommPy.png?branch=master
 .. _Travis: https://secure.travis-ci.org/veeresht/CommPy
-
 .. image:: https://coveralls.io/repos/veeresht/CommPy/badge.svg
-  :target: https://coveralls.io/r/veeresht/CommPy
+:target: https://coveralls.io/r/veeresht/CommPy
+.. image:: https://readthedocs.org/projects/commpy/badge/?version=latest
+:target: https://readthedocs.org/projects/commpy/?badge=latest
+:alt: Documentation Status
 
 
 CommPy