High likelihood it was this: https://wiki.archlinux.org/index.php/Router

The Arch Wiki is pretty awesome, generally, and I used this pretty heavily as a reference. I will say, this was not 100% perfect and I had to use some other outside sources, but most of the info is here.

I did consider writing my own step-by-step post (if for no other reason than for me to not have to remember it), but haven't gotten around to it yet.