add supported python versions

Author: lonelyenvoy

README.md

@@ -1,10 +1,13 @@
 # python-memoization
 
-[![auc][aucsvg]][auc] [![Build Status][travismaster]][travis] [![repository][repositorysvg]][repository] [![License][licensesvg]][license]
+[![Version][aucsvg]][auc] [![Supports Python][pythonsvg]][python] [![Build Status][travismaster]][travis] [![Repository][repositorysvg]][repository] [![License][licensesvg]][license]
 
 [aucsvg]: https://img.shields.io/badge/memoization-v0.0.7-brightgreen.svg
 [auc]: https://github.com/lonelyenvoy/python-memoization
 
+[pythonsvg]: https://img.shields.io/badge/python-2.6,_2.7,_3.2,_3.3,_3.4,_3.5,_3.6,_3.7-brightgreen.svg
+[python]: https://www.python.org
+
 [travismaster]: https://travis-ci.org/lonelyenvoy/python-memoization.svg?branch=master
 [travis]: https://travis-ci.org/lonelyenvoy/python-memoization