I think there should also be some elaboration on the theory of operation wrapped into the answers as well. Questions such as how to "Fit X game on Y screen" feel like a good opportunity to discuss things like active lines of resolution, and why the default options in GroovyMame pick one resolution over another, etc. I've been using groovymame since the very earliest releases, I'd love to help contribute to some documentation.
Looking at Shawn's list, and trying to take a stab at outlining sections, and generalize some sections for questions...
What are GroovyMame and CRTEmudriver?
(Short high-level description of the modification to the emulator and the driver)
What hardware does GroovyMame require?
(Discussion of utilization with Arcade monitors, PVMs, TV, computer monitors, and LCDs), (discussion of known supported video cards).
How does GroovyMame work?
(Brief outline of flow of operation: Driver install, mode generation, instances where per-game command line options are applicable)
(Description of how super resolutions, why it's preferable to generating dozens of specific resolutions)
(Physical limitations of monitor image adjustment, discussion of front porch/back porch tweaking, etc)
(Considerations for mixing rotated vertical games with horizontal games)
An updated installation guide should probably include some specific examples of outdated methodologies of setting up the crtemudriver, since that's changed some over the years, particularly with the introduction of super resolutions.