Update API playground docs (#530)

* add playground config per page

* reword

Author: lawreka

api-playground/mdx/configuration.mdx

@@ -56,6 +56,16 @@ Mintlify allows you to define your API endpoints using a combination of `docs.js
     If you have `server` configured in [docs.json](/settings/global), you can use relative paths like `/v1/endpoint`.
 
     </Note>
+
+    You can also override the globally-defined display mode for the API playground per page by adding `playground` at the top of the MDX file:
+
+    ```md
+    ---
+    title: 'Create new user'
+    api: 'POST https://api.mintlify.com/user'
+    playground: 'none'
+    ```
+    
   </Step>
 
   <Step title="Add your endpoints to your docs">