Add supported Python version badge

Author: dmerejkowsky

README.rst

@@ -5,7 +5,10 @@ Tools for nice user interfaces in the terminal.
 
 .. image:: https://img.shields.io/travis/TankerHQ/python-cli-ui.svg?branch=master
   :target: https://travis-ci.org/TankerHQ/python-cli-ui
-
+  
+.. image:: https://img.shields.io/pypi/pyversions/cli-ui.svg
+  :target: https://pypi.org/project/python-cli-ui
+   
 .. image:: https://img.shields.io/pypi/v/cli-ui.svg
   :target: https://pypi.org/project/cli-ui/