config/graphical-session/graphics-drivers/nvidia: rewrite nouveau

[wbohrer]

Mesa's NVK driver is getting better and more popular. Time to add instructions in the handbook for it. Went ahead and divided the nouveau section into subsections like the other driver pages.

Note that the section divisions are unnecessary for the proprietary driver because it unifies all of the APIs into one package.

[wbohrer]

Argh, I am also failing linkcheck locally from timeout errors for GNU Savannah and ArchWiki. I additionally verified that I cannot access these sites in the browser. Might be more DDoS outages.
Well, I'll go ahead and push requested changes anyway. Actions will probably fail with timeout errors again.

[wbohrer]

I ripped the whole explanation about the technical differences between the xf86-video-nouveau and modesetting Xorg drivers from the old section. I'm thinking it's not necessary at all. It could be replaced with just one sentence explaining that xf86-video-nouveau could be more performant.