This will cover for people that wants to use a Steam overlay for this game as a Non-Steam game. Hopes this helps you out, and if you get stuck somewhere or questions just ask, and I reply soon as I can. 

This guide is intended for all players. It covers many important aspects of the game. I HIGHLY RECOMMEND EVERYONE READS THIS! NOTE: THIS GUIDE IS NOT MINE, I SIMPLY GOT PERMISSION TO POST IT HERE. 

This guide is for new players to learn how to play Co-op mode.