Update index.mdx

added dart title in code block

src/pages/[platform]/start/quickstart/index.mdx

@@ -1481,7 +1481,7 @@ dependencies:
 
 After adding the dependencies, import the dependency and the model provider at the top of main.dart.
 
-```
+```dart title="main.dart"
 import 'package:amplify_api/amplify_api.dart';
 import 'models/ModelProvider.dart';
 ```