add note about legacy fine tuning (#729)

examples/Chat_finetuning_data_prep.ipynb

@@ -9,7 +9,9 @@
     "# Data preparation and analysis for chat model fine-tuning\n",
     "\n",
     "This notebook serves as a tool to preprocess and analyze the chat dataset used for fine-tuning a chat model. \n",
-    "It checks for format errors, provides basic statistics, and estimates token counts for fine-tuning costs.\n"
+    "It checks for format errors, provides basic statistics, and estimates token counts for fine-tuning costs.\n",
+    "The method shown here corresponds to [legacy fine-tuning](https://platform.openai.com/docs/guides/legacy-fine-tuning) for models like babbage-002 and davinci-002.\n",
+    "For fine-tuning gpt-3.5-turbo, see [the current fine-tuning page](https://platform.openai.com/docs/guides/fine-tuning)."
    ]
   },
   {