update nix-darwin to be flake-based

nix/system/worktop/flake.nix

@@ -0,0 +1,41 @@
+{
+  description = "Worktop darwin system";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+
+    nix-darwin.url = "github:nix-darwin/nix-darwin/master";
+    nix-darwin.inputs.nixpkgs.follows = "nixpkgs";
+
+    home-manager.url = "github:nix-community/home-manager";
+    home-manager.inputs.nixpkgs.follows = "nixpkgs";
+
+    variables = {
+      url = "./secret-variables.nix";
+      flake = false;
+    };
+  };
+
+  outputs = inputs@{ self, nix-darwin, nixpkgs, home-manager, variables }:
+    let
+      vars = import variables;
+    in {
+    darwinConfigurations."${vars.hostname}" = nix-darwin.lib.darwinSystem {
+      modules = [
+        ./darwin-configuration.nix
+
+        home-manager.darwinModules.home-manager
+        {
+          home-manager.useGlobalPkgs = true;
+          home-manager.useUserPackages = true;
+          home-manager.users.haak = {
+	    imports = [
+	      ../../home/commandline.nix
+	      ../../home/programs/alacritty
+	    ];
+          };
+        }
+      ];
+    };
+  };
+}