Indie game storeFree gamesFun gamesHorror games
Game developmentAssetsComics

adding the setting to the app would not let you adjust it in-game, you'd still have to tab out and change it in the app. Personally I think a setting like this is best left your desktop environment to set. I think it's probably more worth it to request developers to add setting for configuring the mouse sensitivity, since ideally you don't want to change the system mouse settings just to play one game.