Revert "Removed python2 support mention from README (kivy#2162)"

This reverts commit 3bdeaca.

Author: brvier

README.md

@@ -13,6 +13,7 @@ dependencies you want, and bundle it in an APK along with your own code.
 
 Features include:
 
+-  Support for building with both Python 2 and Python 3.
 -  Different app backends including Kivy, PySDL2, and a WebView with
    Python webserver.
 -  Automatic support for most pure Python modules, and built in support