Nix post-build hooks

[fricklerhandwerk]

Migrate post-build-hook guide to nix.dev. This is a valuable guide that doesn't belong to the Nix reference manual, but should absolutely be preserved and maintained.

More information: NixOS/nix#7979

Note: This is currently blocked on license incompatibility of LGPL and CC-BY-SA.

Blocked by: #478

[fricklerhandwerk]

The goal is to be able to present and maintain different types of documentation the appropriate contexts. One of the measures is to move that article to nix.dev, which requires re-licensing it.

@edolstra @grahamc @endgame @expipiplus1 @thufschmitt @kevinastock according to commit history here and here you are co-authors and therefore copyright holders of that document. Would you agree to re-license it to CC-BY-SA 4.0?

Background:
There was early consensus (mid 2022) for moving in the direction of more cleanly separating documentation types and thus moving things around. November 2022 was another docs team meeting that solidified that understanding. In December 2022 the Nix team merged a change that refers to the Nix Reference Manual, which reflects that agreement across teams.

Edit: Or is re-licensing redundant if we can just refer to the original license in place?

[endgame]

Happy to re-licence but my changes are absolutely trivial. They're only a handful of lines and even GNU would accept changes of that size without copyright paperwork.

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-03-21-documentation-team-meeting-notes-34/26619/1

[asymmetric]

The file used to be named post-build-hook.xml:

❯ git log --pretty="%an" -- doc/manual/advanced-topics/post-build-hook.xml | sort | uniq
Eelco Dolstra
Graham Christensen
Joe Hermaszewski
Kevin Stock
regnat

[grahamc]

and in @grahamc's case word of mouth

ref: NixOS/nix@7c55967

[grahamc]

Note that I am ok with CC-BY-SA but I don't agree with transferring the ownership which is required for contributing it to this repo.

[fricklerhandwerk]

@grahamc Thanks! It looks like we'll remove the CLA soon: #478, I blocked this issue on that.

[thufschmitt]

I'm fine with the re-licencing

[kevinastock]

My change is very minimal, but I'm happy to re-license and/or transfer ownership.