flake: add nixd overlay (providing the nixd package)

[Ruixi-rebirth]

add overlay support

{
  description = "My configuration";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    nixd.url = "github:nix-community/nixd";
  };

  outputs = { nixpkgs, nixd, ... }:
    {
      nixosConfigurations = {
        hostname = nixpkgs.lib.nixosSystem
          {
            system = "x86_64-linux";
            modules = [
              {
                nixpkgs.overlays = [ nixd.overlays.default ];
                environment.systemPackages = with pkgs;[
                  nixd
                ];
              }
            ];
          };
      };
    };
}

[inclyc]

Is this stuff compatible with direnv? Personally I'm using devShells for environmental variables only.

Currently, I think it may not be necessary to introduce new features in flakes. If you like this environment, you can create a local flake and use nix develop your-local-flake-ref#your-shell. It is better to apply upstream changes to everyone.