update readme for pypy/pypy3 support

Author: tony

README.rst

@@ -138,7 +138,7 @@ Project details
 
 ==============  ==========================================================
 tmux support    1.8, 1.9a, 2.0, 2.1, 2.2, 2.3
-python support  2.6, 2.7, >= 3.3
+python support  2.6, 2.7, >= 3.3, pypy, pypy3
 config support  yaml, json, python dict
 Source          https://github.com/tony/tmuxp
 Docs            http://tmuxp.git-pull.com