Add help text for the ping command

Fixes #2487.

src/chat_command_handler.hpp

@@ -88,7 +88,7 @@ class chat_command_handler : public map_command_handler<chat_command_handler>
 		register_command("muteall", &chat_command_handler::do_network_send,
 			_("Mute/Unmute all observers. (toggles)"), "");
 		register_command("ping", &chat_command_handler::do_network_send,
-			"");
+			_("Sends some data to the server. Can be used to verify the network connection and notice disconnects."));
 		register_command("report", &chat_command_handler::do_network_send_req_arg,
 			_("Report abuse, rule violations, etc. to the server moderators. "
 				"Make sure to mention relevant nicknames, etc."), "");