systemd.tmpfiles.rules: Add upstream docs ref

[Kreyren]

Motivation for this change

Being less flustrated with this hell of a lang docs

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• 21.11 Release Notes (or backporting 21.05 Relase 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.

[jtojnar]

As discussed on Matrix, the information is already there, only search.nixos.org displays it incorrectly: NixOS/nixos-search#303. jgm/pandoc#7433 will fix that.

[Mic92]

As discussed on Matrix, the information is already there, only search.nixos.org displays it incorrectly: NixOS/nixos-search#303. jgm/pandoc#7433 will fix that.

What does this mean for this PR so? Having a web url sounds find to me.

[jtojnar]

If we want to merge this as a temporary sort of fix, it would be better if it were formatted as <link xlink:href="https://www.freedesktop.org/software/systemd/man/tmpfiles.d.html"><citerefentry><refentrytitle>tmpfiles.d</refentrytitle><manvolnum>5</manvolnum></citerefentry></link>.

But, hopefully, it will not take too long for the pandoc patch to get merged and we would then have a proper fix with nice formating that would allow us to link to man pages automatically.

[Kreyren]

Closing in favor of NixOS/nixos-search#303 then