Show usage line when no arguments and no --me flag are provided

Previously, running chkip without any arguments attempted to resolve None
as a domain, resulting in misleading output like "No A record".

This commit adds a check to print the usage line if neither a domain nor
the --me flag is specified. This improves usability and makes the tool behave
more predictably when called without arguments.

chkip.py

@@ -216,6 +216,10 @@ def main():
     parser.add_argument("--me", action="store_true", help="Zeigt lokale & öffentliche IPs und prüft auf CGNAT")
     args = parser.parse_args()
 
+    if not args.me and not args.domain:
+        print(parser.format_usage().strip())
+        return
+
     if args.me:
         local_v4, public_v4, public_v6 = get_my_ip()
         result = {