Motivation for this change

tzupdate allows you to update your timezone based on geoip. This is pretty handy for travellers!

I included a service that sets up a one-shot systemd service to update the timezone. I didn't make it start automatically, because I couldn't figure out a way to make it only run after internet access was available.

Additionally, geoip can be somewhat spotty, so having it only run when asked for seems safest.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• 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 nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.