Some updates to the documentation regarding Python 3 and wxPython 4.

This work is not complete and the install and build instructions need to be sanity checked and updated for modern versions of all three platforms.

gui/Scyther/XMLReader.py

@@ -37,7 +37,7 @@ import sys
 # Check for cElementTree presence. Otherwise use ElementTree.
 useiter = True
 try:
-    # python 2.5 has cElementTree in the core
+    # cElementTree is in Python since version 2.5
     import xml.etree.cElementTree as cElementTree
 except:
     # try the old way