Quoted from the Steam FAQ:
What’s the difference between Steam and itch.io version of Buckshot Roulette?
The Steam version of Buckshot Roulette includes localization, controller support, achievements, leaderboards, 4 new items for Double or Nothing mode, free digital copy of the game’s soundtrack. The game will also receive a multiplayer mode later this year!
So, not only do we have to wait for an update, but the Steam players get extra toys to play with...