Generic flake.nix for migrating from shell.nix

flake.nix

{
  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem
      (system:
        let pkgs = nixpkgs.legacyPackages.${system}; in
        {
          devShells.default = import ./shell.nix { inherit pkgs; };
        }
      );
}