Add python versions badge to README

Author: joowani

README.rst

@@ -12,6 +12,10 @@
     :target: https://badge.fury.io/py/python-arango
     :alt: Package Version
 
+.. image:: https://img.shields.io/badge/python-2.7%2C%203.4%2C%203.5-blue.svg
+    :target: https://github.com/joowani/python-arango
+    :alt: Python Versions
+
 .. image:: https://coveralls.io/repos/github/joowani/python-arango/badge.svg?branch=master
     :target: https://coveralls.io/github/joowani/python-arango?branch=master
     :alt: Test Coverage