Issue #25874: Clarify platform support in the "Using Python on Windows" doc.

Thanks to Chris Wilcox for the initial patch.

Doc/using/windows.rst

@@ -24,6 +24,14 @@ core interpreter and library being used by a single user. The installer is also
 able to install for all users of a single machine, and a separate ZIP file is
 available for application-local distributions.
 
+Supported Versions
+------------------
+
+As specified in :pep:`11`, a Python release only supports a Windows platform
+while Microsoft considers the platform under extended support. This means that
+Python 3.5 supports Windows Vista and newer. If you require Windows XP support
+then please install Python 3.4.
+
 Installation Steps
 ------------------
 

Misc/ACKS

@@ -1554,6 +1554,7 @@ Felix Wiemann
 Gerry Wiener
 Frank Wierzbicki
 Santoso Wijaya
+Chris Wilcox
 Bryce "Zooko" Wilcox-O'Hearn
 Timothy Wild
 Jakub Wilk