So, I've got the renderman engine from GitHub and, when I install it and enable it (as an add-on), it doesn't show up with the render engines. Why? (The add-on said it required a 2.8 blender update so the add-on is 2.8 ready) Also, I'm trying it in blender 2.81 and blender 2.82a
Yeah, that is just not going to work. It is actually not compatible with 2.8 or many of the previous versions. Even though it may say. There are forums all over the place that say the same thing. No one has gotten it to work. But, it is probably for the best. Renderman is not near as capable in clarity of pixelization as cycles. 1080p in Cycles vs Rman is a pretty big difference. Plus, I would guess that alot of the modifiers in Blender would not work in Renderman. It also takes alot more time to Render especially in Windows. And a huge bug with Renderman that comes from what people like about it overcasting light, is that you will get pitch black shadows sometimes that you cannot get rid of.