menudata.README: comments added

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@66686 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/xml/menudata.README

@@ -1,3 +1,7 @@
-Find more info about how to add item in the menu:
-http://grass.osgeo.org/programming7/wxguitoolboxes.html
+MENU
+- the entries in menudata.xml and module_tree_menudata.xml are autogenerated 
+  via tools/build_modules_xml.py (see ../Makefile)
 
+TOOLBOXES
+- Find more info about how to add items to the menu:
+  https://trac.osgeo.org/grass/wiki/wxGUIDevelopment/Toolboxes