How to stop annoying High Sierra upgrade prompts in macOS

At 3:28PM ET I made a discovery that will change humanity for the better. Okay, maybe not humanity, but it will certainly make my life better.
I’m using a 2015 MacBook Pro. I bought it last fall because I needed a new computer, and because I need to plug things in all the time, I didn’t want any of the new Macs. This meant that my new old computer came installed with macOS Sierra 10.12.1. I’ve heard nothing but bad things about High Sierra so I’ve been holding off.
But m