feat(genapi): add recommendations for structured outputs usage

Author: fpagny

pages/generative-apis/how-to/use-structured-outputs.mdx

@@ -132,6 +132,13 @@ Output example:
 }
 ```
 
+<Message type="tip">
+    Structured outputs accuracy may vary between models. For instance, with Llama models, we suggest adding a description of the field looked for in `response_format` and in `system` or `user` messages. In our example this would mean adding a system prompt similar to:
+    ```bash
+    "content": "The following is a voice message transcript. Provide the message title, summary and action items. Only answer in JSON using '{' as the first character.",
+    ```
+</Message>
+
 ### Using structured outputs with JSON schema (manual definition)
 
 Alternatively, users can manually define the JSON schema inline when calling the model.