Just what it says on the tin – Increases the number of Resitance Order Cards you get when you first meet each faction.
this by default increases that to 4.
this can be changed in the XComGameData.ini config file.
each faction has a potential 17 (or 18 for skirmishers) cards, but you also get some from improving influence, covert ops and continent bonuses. I don't know what the highest "safe" value is.
there's also an optional bit in the config which will give each faction +1 card slot.