Tweak an informative message that has mislead at least 3 people so far.

depot_tools/git_cl/git_cl.py

 #!/usr/bin/python
 # git-cl -- a git-command for integrating reviews on Rietveld
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 import errno
 import logging
 import optparse
 import os
 import re
 import subprocess
@@ skipping 1011 matching lines @@
     if os.path.isfile(hook):
       RunHook(hook, upstream_branch=base_branch, error_ok=True)
 
   return 0
 
 
 @usage('[upstream branch to apply against]')
 def CMDdcommit(parser, args):
   """commit the current changelist via git-svn"""
   if not settings.GetIsGitSvn():
-    print('This doesn\'t appear to be an SVN repository.')
-    print('Are you sure you didn\'t mean \'git cl push\'?')
+    message = """This doesn't appear to be an SVN repository.
+If your project has a git mirror with an upstream SVN master, you probably need
+to run 'git svn init', see your project's git mirror documentation.
+If your project has a true writeable upstream repository, you probably want
+to run 'git cl push' instead.
+Choose wisely, if you get this wrong, your commit might appear to succeed but
+will instead be silently ignored."""
+    print(message)
     raw_input('[Press enter to dcommit or ctrl-C to quit]')
   return SendUpstream(parser, args, 'dcommit')
 
 
 @usage('[upstream branch to apply against]')
 def CMDpush(parser, args):
   """commit the current changelist via git"""
   if settings.GetIsGitSvn():
     print('This appears to be an SVN repository.')
     print('Are you sure you didn\'t mean \'git cl dcommit\'?')
@@ skipping 217 matching lines @@
             ('AppEngine is misbehaving and returned HTTP %d, again. Keep faith '
              'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
   # Not a known command. Default to help.
   GenUsage(parser, 'help')
   return CMDhelp(parser, argv)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))