pipes: add documentation for pipes

Stick with the name "gdb_port" even if this command
can be used for other things(disable, named pipes,
anonymous stdin/out pipe). "port" is correct for
probably more than 90% of use cases, if not more.

Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

src/server/telnet_server.c

@@ -619,7 +619,7 @@ static const struct command_registration telnet_command_handlers[] = {
 		.mode = COMMAND_ANY,
 		.help = "Specify port on which to listen "
 			"for incoming telnet connections.  "
-			"No arguments reports telnet port; zero disables.",
+			"Read help on 'gdb_port'.",
 		.usage = "[port_num]",
 	},
 	COMMAND_REGISTRATION_DONE