The mod would, as the name implies, place a workshop in the Railroad HQ that can be activated once you have completed 'Tradecraft', destroyed the Institute, or wiped out the Railroad. It would have everything a normal settlement would have, except Bunker hill Caravans, supply lines, and recruitment beacons. There is already a mod out that adds a workshop to the Institute, and I'm sure one is coming for the Prydwen too, so why not the Railroad HQ?