The following solution is from TrueAchievements, posted by JordanTheBigBoy
This is a simple story progression quest that appears after you complete the main story line of the DLC (or at least the "The Way Life Should Be" route).
Very self explanatory, but I'm only stating this because I was paranoid that I was missing something until it finally appeared at the end.
It has been pointed out by Kennyannydenny that this could be missed if you tattle on Acadia to The Institute or the Brotherhood of Steel. That is a miscellaneous objective and if you do that you're a monster.