launcher: warn when verification is disabled

Make it clear(er) to the user that this option is dangerous.

Bug: https://crbug.com/gerrit/11045
Change-Id: I5580996c26653a7c823b69008de3626abf1b0068
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/257333
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: David Pursehouse <dpursehouse@collab.net>

repo

@@ -525,6 +525,9 @@ def _Init(args, gitc_init=False):
   try:
     if not opt.repo_verify:
       do_verify = False
+      print('repo: warning: verification of repo code has been disabled;\n'
+            'repo will not be able to verify the integrity of itself.\n',
+            file=sys.stderr)
     else:
       if NeedSetupGnuPG():
         do_verify = SetupGnuPG(opt.quiet)