How do you add friends in-game??

[Pèpè Silvia]

So I was playing coop last night with some random person, but we couldn't find any way to add each other to friends thru the game.
Is there any way to do that so we don't have to go search around for each other in steam and the like?

[Green777]

if they come into you game just use the in game invite, if they accept you should see each other on the main map as long as you have the friends on in your game