added some utilities and going to nh

nixos/system/users.nix

@@ -1,7 +1,11 @@
-{ ... }:
+{ pkgs, ... }:
 {
+  # Required so fish is registered in /etc/shells and gets the NixOS environment.
+  programs.fish.enable = true;
+
   users.users.prouk = {
     isNormalUser = true;
     extraGroups = [ "wheel" ];
+    shell = pkgs.fish;
   };
 }