fix readme on nested_params for response format

Author: aaaugustine29

README.md

@@ -373,19 +373,28 @@ Nested parameters are dictionaries, typed using `TypedDict`, for example:
 
 ```python
 from openai import OpenAI
+from pydantic import BaseModel
 
 client = OpenAI()
 
-response = client.chat.responses.create(
+class CalendarEvent(BaseModel):
+    name: str
+    date: str
+    participants: list[str]
+
+response = client.responses.parse(
+    model="gpt-4o-2024-08-06",
     input=[
+        {"role": "system", "content": "Extract the event information."},
         {
             "role": "user",
-            "content": "How much ?",
-        }
+            "content": "Alice and Bob are going to a science fair on Friday.",
+        },
     ],
-    model="gpt-4o",
-    response_format={"type": "json_object"},
+    text_format=CalendarEvent,
 )
+
+event = response.output_parsed
 ```
 
 ## File uploads