Add a guide through enrolling MOK

[karajan9]

Since I never before had to interact with MOK I was pretty lost when I had to navigate through the options of the MOK management (I use NVIDIA drivers).
I was equally lost when I had to look up a guide, missed the timeout, and didn't know how to get the screen back.

I had read https://universal-blue.org/installation/#secure-boot but it doesn't provide much guidance. I found https://en.opensuse.org/SDB:NVIDIA_drivers#Secureboot to be a good help, it answers both questions, with pretty pictures. Maybe include something similar, or just a link there?

If you know what you'd like I can make a PR.

[akdev1l]

This sounds like a great idea imo

[castrojo]

A PR would be amazing, thank you!