Update json-endpoint.mdx

added note about incurring workers ai usage when using json endpoint

Author: kathayl

src/content/docs/browser-rendering/rest-api/json-endpoint.mdx

@@ -15,6 +15,12 @@ The `/json` endpoint extracts structured data from a webpage. You can specify th
 | prompt          | no        | Must supply one of `prompt` or `response_format`.                            |
 | response_format | no        | Must supply one of `prompt` or `response_format`. May include a JSON schema. |
 
+:::note[Note]
+
+The `/json` endpoint leverages [Workers AI](/workers-ai/) for data extraction. Using this endpoint incurs usage on Workers AI, which you can monitor usage through the Workers AI Dashboard.
+
+:::
+
 ## Basic Usage
 
 ### With a Prompt and JSON schema