Clarify options that control the repo executable version

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/subcmds/sync.py b/subcmds/sync.py
index 55ffca3..b5cc604 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -66,10 +66,11 @@
                  dest='detach_head', action='store_true',
                  help='detach projects back to manifest revision')
 
-    p.add_option('--no-repo-verify',
+    g = p.add_option_group('repo Version options')
+    g.add_option('--no-repo-verify',
                  dest='no_repo_verify', action='store_true',
                  help='do not verify repo source code')
-    p.add_option('--repo-upgraded',
+    g.add_option('--repo-upgraded',
                  dest='repo_upgraded', action='store_true',
                  help=SUPPRESS_HELP)