Fix UA flag setting (and set more of them)

certbot/cli.py

@@ -1108,7 +1108,9 @@ def _create_subparsers(helpful):
              "plugin and use case, and to know when to deprecate support for past Python "
              "versions. If you wish to hide this information from the Let's "
              'Encrypt server, set this to "". '
-             '(default: {0})'.format(sample_user_agent()))
+             '(default: {0}). The flags encoded in the user agent are: '
+             '--duplicate, --force-renew, --allow-subset-of-names, -n, and '
+             'whether any hooks are set.'.format(sample_user_agent()))
     helpful.add("certonly",
                 "--csr", type=read_file,
                 help="Path to a Certificate Signing Request (CSR) in DER or PEM format."