(Running a 64bit system, your Fallout 4 data folder SHOULD be here: C:\Program Files (x86)\Steam\steamapps\common\Fallout 4\Data)
Drop these files into your Fallout 4 Data folder, and type the following command/s in your console:
bat sett1 (Adds 1 Settler)
bat sett2 (Adds 5 Settlers)
bat sett3(Adds 10 Settlers)
If you are having issues getting the NPCs to work/spawn above 20 settlers, you can try manually setting your character's charisma using the batch file below. Personally, I don't recommend this as it can sometimes result in bugged saves, so really you should use this: https://www.nexusmods.com/fallout4/mods/1613
If you don't want to install another mod, run the "bat charismaboost" command included in the mod (remember to use at your own risk).
After spawning in the setters, you have to assign them to a settlement or they just kinda stand there. Look at the settler, press R, select settlement of choice.