📝 Update docs for ORJSONResponse with details about improving performance (#2615)

Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>

docs_src/custom_response/tutorial001b.py

@@ -6,4 +6,4 @@ app = FastAPI()
 
 @app.get("/items/", response_class=ORJSONResponse)
 async def read_items():
-    return [{"item_id": "Foo"}]
+    return ORJSONResponse([{"item_id": "Foo"}])