This small settlement area is found in a literal alley. It's initially occupied by raiders which you'll need to clear first as part of the sidequest "Taking Point: Hangman’s Alley".
This alley has a cooking station and weapons workbench. This settlement has a very limited space to build Water or Food supplies so make sure to set up a supply line immediately. You can also clear out the existing walls and roofs to clear some much needed space.
I can't get recruitment beacon built I think it bugged