guest: add guest user

nixos/configuration.nix

@@ -100,6 +100,17 @@
     ];
   };
 
+  users.users.guest = {
+    isNormalUser = true;
+    description = "Guest Account";
+    extraGroups = [ "networkmanager" ];
+    shell = pkgs.zsh;
+    packages = with pkgs; [
+      mpv
+      vlc
+    ];
+  };
+
   # Install firefox.
   programs.firefox.enable = true;