add systems

modules/systems/nix/darwin.nix

@@ -0,0 +1,16 @@
+{
+  nix.gc = {
+    automatic = true;
+    interval = [
+      {
+        Weekday = 7;
+        Hour = 3;
+        Minute = 15;
+      }
+    ];
+    options = "--delete-older-than 14d";
+  };
+
+  nix.settings.auto-optimise-store = true;
+  nix.optimise.automatic = true;
+}