Update help text for git-map-branches

R=lgarron@chromium.org

Bug: 758435
Change-Id: I557cf5027636e8cf30d3971071723bf2b9333f9e
Reviewed-on: https://chromium-review.googlesource.com/639036Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

git_map_branches.py

@@ -307,7 +307,8 @@ def main(argv):
 
   parser = argparse.ArgumentParser()
   parser.add_argument('-v', action='count',
-                      help='Display branch hash and Rietveld URL')
+                      help=('Pass once to show tracking info; '
+                           'twice for hash and review url'))
   parser.add_argument('--no-color', action='store_true', dest='nocolor',
                       help='Turn off colors.')
   parser.add_argument(