Migrating [some of] the NixOS on ARM documentation

[samueldr]

Issue description

From #33745.

It'd be best if some of the ARM documentation was found in the upstream NixOS manual.

I do not think, though, that the current manual implementation is enough to completely subsume the use of the wiki. I'm thinking that the misc. platform notes are likely not good for documentation in the manual.

Let's figure out a scheme for documenting this in the manual, as much as possible, while not duplicating work with the Wiki.

[stale]

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[samueldr]

I don't think the manuals are the right location for most of the "on ARM" documentation as it stands today.

Only a few things would be relevant, and truthfully, it'd be "hey, we're working on fixing this to work just like on x86_64".

Anything else is mostly device-specific, unsupported or troubleshooting.

• https://wiki.nixos.org/wiki/NixOS_on_ARM