I have had very nice results adding cold brewed coffee to the keg at packaging. If you bottle, you can add it then. I like to make a nice robust cold brew with about 1 cup of coffee grounds to 4 cups of water steeped 24 hrs in the fridge. I usually add at least a cup of this to a keg, but not a full 5 gals...typically, 4 gals or so. I would think the coffee would get lost if added in the boil, and the character would be different. Dry bean in the fermenter or cold brew seem to be the most popular and efficient ways.