Update develop/parachains/maintenance/asynchronous-backing.md

Co-authored-by: Nicolás Hussein <[email protected]>

Author: brunopgalvao

develop/parachains/maintenance/asynchronous-backing.md

@@ -130,7 +130,7 @@ async backing system.
 
     - Add the dependency `cumulus-primitives-aura` to the `runtime/Cargo.toml` file for your runtime
 
-    ```rust
+    ```rust title="Cargo.toml"
     ..
     cumulus-primitives-aura = { path = "../../../../primitives/aura", default-features = false }
     ..