neovim.url = github:neovim/neovim?dir=contrib;

https://github.com/NixOS/nixpkgs

???
# nix-env -iA
# nixos.nixUnstable

https://www.paretooptimal.dev/installing-nixos-using-devos-and-nix-flakes/
    nixos-install --flake .#NixOS