Update "Prerequisites" to describe Melange as written in Python 2.7.

It may have started on 2.5, but we are all 2.7 now and quite happy
to have broken with the past. :-)

Also the installation link is dropped. Readers are responsible for
foundational things like "having access to a workstation on which
Python is installed".

GettingStarted.wiki

diff --git a/GettingStarted.wiki b/GettingStarted.wiki
index 867a80d..12d89d2 100644
--- a/GettingStarted.wiki
+++ b/GettingStarted.wiki
@@ -5,7 +5,7 @@
 
 = Prerequisites =
 
-[MelangeIntro Melange] is a web application written in python 2.5/2.6/2.7 ([http://www.python.org/download/releases/2.5.5/ install]) that runs on
+[MelangeIntro Melange] is a web application written in Python 2.7 that runs on
 [http://code.google.com/appengine/ Google App Engine].
 
 = TL;DR =