mandoc: change OSNAME to Nixpkgs to match groff

[sternenseemann]

Description of changes

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.05 Release Notes (or backporting 22.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[pennae]

looks good. we'd prefer to keep the nixos-specific manpages at saying they're for nixos, but we're fine having it either way as long as it's consistent.

[pennae]

side note for completeness:

nixpkgs/pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs/options.py

Line 380 in 417dd2a

r'''.TH "CONFIGURATION\&.NIX" "5" "01/01/1980" "NixOS" "NixOS Reference Pages"''',

also hard-codes nixos into a manpage, but since so far this manpage is generated by a nixos module for a nixos system we'd argue it shouldn't be changed (and when it is, changed to being a free parameter that the module sets to NixOS)

[sternenseemann]

@pennae I was contemplating making a mandoc-nixos, man-db-nixos attribute that is used in the respective NixOS modules, so that the entry at the bottom makes sense – could also be nice for generating the HTML pages at some point for the website/manual.

In general, I do feel that if nixos-install(8) was included in OpenBSD, the thing at the bottom should probably read OpenBSD for better or worse as it's the “normal” way of doing things.

[pennae]

@sternenseemann not sure about that to be honest, having these variants would introduce a rendering discrepancy depending on how mandoc/groff are installed (seeing how nix{ ,-}shell takes priority over systemPackages). we'd rather have everything consistent independent of how the renderer was installed. using a special package specifically for rendering html pages to be published online sounds reasonable though.

the only thing we really want to not change at this point is configuration.nix.5 due to its specificity, everything else as you've mentioned can really run and be useful anywhere.