Fix help string: TLD -> 2LD

Author: coldfix

README.rst

@@ -96,7 +96,7 @@ certbot's command line:
                                          | netcup API client session times out.
                                          | (Default: 3, Recommended: >= 1)
 
-``--dns-netcup-zone-name DOMAIN``        | Zone name to operate on (often TLD).
+``--dns-netcup-zone-name DOMAIN``        | Zone name to operate on (often second-level-domain).
                                          | Will be determined using brute-force
                                          | requests if not specified.
 ======================================== =======================

certbot_dns_netcup.py

@@ -46,7 +46,7 @@ def add_parser_arguments(cls, add):
         add('login-retries', default=3, type=int,
             help="login retry attempts in case of session timeout")
         add('zone-name', help=(
-            "zone name to operate on (often TLD). "
+            "zone name to operate on (often second-level-domain). "
             "Will be determined using brute-force requests if not specified."))
 
     def more_info(self):