Bump README python requirement to 2.6.0.

The code already checks for python 2.6.

doc/README

@@ -5,7 +5,7 @@ Currently it produces only HTML output with tables and graphs.
 
 Requirements
 ============
-- Python (>= 2.4.4)
+- Python (>= 2.6.0)
 - Git (>= 1.5.2.4)
 - Gnuplot (>= 4.0.0)
 - a git repository (bare clone will work as well)