Clarify Python 2.7 for Windows is not supported

Author: UCHINO Tatsunori

Diff for: README.md

@@ -85,7 +85,7 @@ to see if you get results in `test/` direcotry.
   - Linux Ubuntu 16.04/14.04
   - Windows (thanks to [wuaalb](https://github.com/wuaalb))
 - Python
-  - 2.7
+  - 2.7 (Windows is currently not supported)
   - 3.6/3.5
   - Required packages
     - Cython 0.24 (or later versions; required)