Extend documentation for `git map-branches`

Document the -v and --no-color options.

R=iannucci@chromium.org

Change-Id: I07624403f591b23cc5701aa8201124fdfdb65781
Reviewed-on: https://chromium-review.googlesource.com/c/1360710
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
diff --git a/git_map_branches.py b/git_map_branches.py
index 8627b37..00e204b 100755
--- a/git_map_branches.py
+++ b/git_map_branches.py
@@ -307,8 +307,9 @@
 
   parser = argparse.ArgumentParser()
   parser.add_argument('-v', action='count',
-                      help=('Pass once to show tracking info; '
-                           'twice for hash and review url'))
+                      help=('Pass once to show tracking info, '
+                            'twice for hash and review url, '
+                            'thrice for review status'))
   parser.add_argument('--no-color', action='store_true', dest='nocolor',
                       help='Turn off colors.')
   parser.add_argument(