feat(fish): add Borderlands save write-protection toggle

configs/nixos/modules/shell/fish/default.nix

@@ -30,6 +30,7 @@ in
     home-manager.users.${user} = {
       home.packages = with pkgs; [
         bat # backs the manpager
+        e2fsprogs # provides chattr and lsattr for the readonly function
         fastfetch # the shell greeting
       ];
 
@@ -99,6 +100,11 @@ in
             body = builtins.readFile ./functions/deploy-to.fish;
           };
 
+          readonly = {
+            description = "Toggle write protection for a Borderlands 2 save";
+            body = builtins.readFile ./functions/readonly.fish;
+          };
+
         };
 
         # Rendered by home-manager into ~/.config/fish/config.fish.