Better document how to specify a port when using TCP connection

Fixes #868

Also, fix a pylint complaint.

meshtastic/__main__.py

@@ -1621,10 +1621,12 @@ def addConnectionArgs(parser: argparse.ArgumentParser) -> argparse.ArgumentParse
         "--host",
         "--tcp",
         "-t",
-        help="Connect to a device using TCP, optionally passing hostname or IP address to use. (defaults to '%(const)s')",
+        help=("Connect to a device using TCP, optionally passing hostname or IP address to use. (defaults to '%(const)s'). "
+              "A port number may be specified as well, e.g. meshtastic.local:4404. The default port is 4403."),
         nargs="?",
         default=None,
         const="localhost",
+        metavar="HOST[:PORT]",
     )
 
     group.add_argument(

meshtastic/tests/test_main.py

@@ -3157,7 +3157,7 @@ def test_main_ota_update_file_not_found(capsys):
 
     assert pytest_wrapped_e.type == SystemExit
     assert pytest_wrapped_e.value.code == 1
-    out, err = capsys.readouterr()
+    out, _ = capsys.readouterr()
     assert "OTA firmware file not found" in out
     assert "/nonexistent/firmware.bin" in out