Create documentation for nixos and wayland/hyprland setup

I realised I solved several issues to get this working on nixos and hyprland so I should share that info when I get back to the desk.

I could provide a flake for the repo, or just document steps here for anyone searching

---

Search keywords for posterity: FHS, XDG, nix, nixos, steam-run, lld, ld, dynamic linker, nix-ld