Improve description for retrieve events response

Author: xvaier

docs/api-reference/v2/endpoints/activities/get-activities-.mdx

@@ -5,4 +5,10 @@ title: Retrieve Event
 
 <Note>
 For backwards compatibility, this endpoint is also available as `/firework/v2/activities/{index}/{source}/{id}`.
-</Note>
+</Note>
+
+<ResponseExample>
+```json Response Example
+This response changes based on the event type.
+```
+</ResponseExample>