[docs] [issue9442] Update sys.version doc

Martin v. Löwis <martin@v.loewis.de> added the comment: Ask yourself: what are the first three characters? If that's not clear, type sys.version[:3]. Is it still unclear what this is talking about? ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue9442> _______________________________________