Update minimal Python version to 2.7 (#4207)

diff --git a/python/README.md b/python/README.md
index 4c19429..4b48225 100644
--- a/python/README.md
+++ b/python/README.md
@@ -30,7 +30,7 @@
 Installation
 ============
 
-1) Make sure you have Python 2.6 or newer.  If in doubt, run:
+1) Make sure you have Python 2.7 or newer.  If in doubt, run:
 
        $ python -V