Add instructions to install nix with a package manager.

[loreb]

Prompted by #194

This came out longer than I hoped; feel free to criticize it to death (or merge and then modify to your pleasure).

[github-actions]

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[loreb]

I have read the CLA Document and I hereby sign the CLA

[loreb]

Slightly rewritten because I forgot a step (it didn't show in my history because I ran it as root).

[fricklerhandwerk]

This needs a proper rebase, these files don't exist any more. @SuperSandro2000 Would you like to continue with reviews?

@loreb sorry for the outrageous turnaround on your PR. Now that we have an active documentation team, it should all go much faster.

[loreb]

@fricklerhandwerk np, shit happens

If you feel like rewriting the thing yourself be my guest, it's basically:

1. install using your package manager (because maintainers made sure it works)
2. may or may not need to enable the nix service depending on distribution (some distros will not start a service unless you personally say so)
3. will likely need to set a few environment variables by sourcing some file, hopefully /etc/profile.d/nix-something.sh, maybe /usr/share/examples/nix/whatever.sh or similar (eg debian)
4. subscribe to a channel and nix-channel --update
5. double check if there are distro-specific instructions (eg debian&arch require users to be part of a group)

[fricklerhandwerk]

Discussed in Nix documentation team meeting:

• problem is really with who would own and maintain it, and it's not a priority for us
• adding usage paths with complicated system interactions will increase maintenance burden
  • we don't have the capacity for taking care of that
• not entirely clear where that documentation should even live
• since we're won't be able to maintain it, best move it to the NixOS User Wiki if you care about preserving that information (which we think is valuable)
• closing

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-06-26-documentation-team-meeting-notes-58/29666/1