Sets the iWorkshopSettlerPopulationMax to a higher value. Options of 50, 100, 500, and 999. I personally use 50. Managing that many people will be a bitch anyways. You can always upgrade later and I don't know how this affects the rate at which settlers arrive.

[INSTALL]
Locate 'Fallout4Prefs.ini' in your 'Documents/My Games/Fallout 4' folder.
Add 'bEnableFileSelection=1' after the [Launcher] tag.
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Place esp in 'steamapps\common\Fallout 4\Data'.
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Locate 'plugins.txt' in your 'AppData\Local\Fallout4' folder.
Add 'IncreasedSettlerPopulation50.esp' (or your selected option) on a new line after 'Fallout4.esm'.