Update flake

nix/flake.nix

@@ -3,17 +3,53 @@
 
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    nix-darwin.url = "github:LnL7/nix-darwin";
+    nix-darwin.inputs.nixpkgs.follows = "nixpkgs";
     home-manager = {
       url = "github:nix-community/home-manager";
       inputs.nixpkgs.follows = "nixpkgs";
     };
   };
 
-  outputs = { nixpkgs, home-manager, ... }:
+  outputs = { self, nix-darwin, nixpkgs, home-manager, ... }:
     let
       system = "x86_64-darwin";
       pkgs = nixpkgs.legacyPackages.${system};
+
+      configuration = { pkgs, ... }: {
+        environment.systemPackages =
+          [
+            pkgs.vim
+          ];
+
+        # Auto upgrade nix package and the daemon service.
+        services.nix-daemon.enable = true;
+        # nix.package = pkgs.nix;
+
+        nix.settings.experimental-features = "nix-command flakes";
+
+        programs.zsh.enable = true;  # default shell on catalina
+
+        # Set Git commit hash for darwin-version.
+        system.configurationRevision = self.rev or self.dirtyRev or null;
+
+        # Used for backwards compatibility, please read the changelog before changing.
+        # $ darwin-rebuild changelog
+        system.stateVersion = 4;
+
+        # The platform the configuration will be used on.
+        nixpkgs.hostPlatform = system;
+      };
     in {
+      # Build darwin flake using:
+      # $ darwin-rebuild build --flake .#Martins-MacBook-Pro
+      darwinConfigurations."Martins-MacBook-Pro" = nix-darwin.lib.darwinSystem {
+        modules = [ configuration ];
+      };
+
+      # Expose the package set, including overlays, for convenience.
+      darwinPackages = self.darwinConfigurations."Martins-MacBook-Pro".pkgs;
+
       homeConfigurations = { 
         "moustachioed" = home-manager.lib.homeManagerConfiguration {
           inherit pkgs;