Note that latest Python is unsupported on Windows XP

Thanks Dan A.

installation.md

@@ -7,6 +7,8 @@ When we refer to "Python 3" in this book, we will be referring to any version of
 Visit https://www.python.org/downloads/ and download the latest version. At the time of this writing, it was Python 3.5.1 
 The installation is just like any other Windows-based software.
 
+Note that if your Windows version is pre-Vista, you should [download Python 3.4 only](https://www.python.org/downloads/windows/) as later versions require newer versions of Windows.
+
 CAUTION: Make sure you check option `Add Python 3.5 to PATH`.
 
 To change install location, click on `Customize installation`, then `Next` and enter `C:\python35` as install location.