docs: qa rag nit (#16400)

docs/docs/use_cases/question_answering/chat_history.ipynb

@@ -359,11 +359,20 @@
     "Here we've gone over how to add application logic for incorporating historical outputs, but we're still manually updating the chat history and inserting it into each input. In a real Q&A application we'll want some way of persisting chat history and some way of automatically inserting and updating it.\n",
     "\n",
     "For this we can use:\n",
+    "\n",
     "- [BaseChatMessageHistory](/docs/modules/memory/chat_messages/): Store chat history.\n",
     "- [RunnableWithMessageHistory](/docs/expression_language/how_to/message_history): Wrapper for an LCEL chain and a `BaseChatMessageHistory` that handles injecting chat history into inputs and updating it after each invocation.\n",
     "\n",
     "For a detailed walkthrough of how to use these classes together to create a stateful conversational chain, head to the [How to add message history (memory)](/docs/expression_language/how_to/message_history) LCEL page."
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "1f67a60a-0a31-4315-9cce-19c78d658f6a",
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {