Add better descripion of subscribe_room_many command

src/mod_muc_admin.erl

@@ -336,6 +336,7 @@ get_commands_spec() ->
 			result = {nodes, {list, {node, string}}}},
      #ejabberd_commands{name = subscribe_room_many, tags = [muc_room],
 			desc = "Subscribe several users to a MUC conference",
+			longdesc = "This command accept up to 50 users at once (this is configurable with `subscribe_room_many_max_users` option)",
 			module = ?MODULE, function = subscribe_room_many,
 			args_desc = ["Users JIDs and nicks",
                                      "the room to subscribe",