added some utilities and going to nh

nixos/programs/nh.nix

@@ -0,0 +1,9 @@
+{ ... }:
+{
+  # nh: nicer frontend for nixos-rebuild / nix-collect-garbage.
+  # Cleanup stays on nix.gc (see system/nix.nix) to avoid two GC timers.
+  programs.nh = {
+    enable = true;
+    flake = "/home/prouk/flake";
+  };
+}