howto_release: add trac milesstone update

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@67602 15284696-431f-4ddb-bdfa-cd5b030d7da7

doc/howto_release.txt

@@ -153,6 +153,9 @@ Contents
       - store in trac: http://trac.osgeo.org/grass/wiki/Release/7.XX.YY-News
       - store in Web as announces/announce_grass$MAJOR$MINOR$RELEASE.html <- how? with protected PHP upload page?
 
+     full release:
+      - update trac milesstone/add next: https://trac.osgeo.org/grass/admin/ticket/milestones
+
  o upload user HTML manual in case of *final release* from compiled English
    version at (warning: needs stuff to be compiled).
       - download new source code package, compile with most settings