[Doc] Add data ingestion clarification for AIR converting existing py…

…torch code example (ray-project#32058)

The example under Ray AI Runtime/Example section directly used native PyTorch datasets for data loading. It's good to clarify that the current approach is for simplicity, the more recommended approach is to use the Ray dataset.

Signed-off-by: Yunxuan Xiao <yunxuanx@Yunxuans-MBP.local.meter>
Signed-off-by: Yunxuan Xiao <xiaoyunxuan1998@gmail.com>
Co-authored-by: Yunxuan Xiao <yunxuanx@Yunxuans-MBP.local.meter>
Co-authored-by: angelinalg <122562471+angelinalg@users.noreply.github.com>
Co-authored-by: Yunxuan Xiao <yunxuanx@Yunxuans-MacBook-Pro.local>
Signed-off-by: Edward Oakes <ed.nmi.oakes@gmail.com>

doc/source/ray-air/examples/convert_existing_pytorch_code_to_ray_air.ipynb

@@ -59,11 +59,14 @@
    ]
   },
   {
+   "attachments": {},
    "cell_type": "markdown",
    "id": "db36ae56",
    "metadata": {},
    "source": [
-    "Then we download the data:"
+    "Then we download the data: \n",
+    "\n",
+    "This tutorial assumes that your existing code is using the `torch.utils.data.Dataset` native to PyTorch. It continues to use `torch.utils.data.Dataset` to allow you to make as few code changes as possible. **This tutorial also runs with Ray Data, which gives you the benefits of efficient parallel preprocessing.** See an example of using Ray Data for the CIFAR-10 dataset {doc}`here </ray-air/examples/torch_image_example>`."
    ]
   },
   {
@@ -1300,7 +1303,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 3.8.10 ('venv': venv)",
+   "display_name": "Python 3",
    "language": "python",
    "name": "python3"
   },
@@ -1314,11 +1317,11 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.8.10"
+   "version": "3.9.6 (default, Oct 18 2022, 12:41:40) \n[Clang 14.0.0 (clang-1400.0.29.202)]"
   },
   "vscode": {
    "interpreter": {
-    "hash": "3c0d54d489a08ae47a06eae2fd00ff032d6cddb527c382959b7b2575f6a8167f"
+    "hash": "31f2aee4e71d21fbe5cf8b01ff0e069b9275f58929596ceb00d14d90e3e16cd6"
    }
   }
  },