Run game with mangohud

MangoHud is the performance monitoring overlay used on the Steam Deck.

To run game with mangohud simply set MANGOHUD=1 environment variable

In steam you can set launch command of game to this:

 MANGOHUD=1 %command%

If you're using gamescope it has mangohud built in; you have to pass this argument to gamescope instead of using the env var:

--mangoapp