Add to panel serve docs #611 (#614)

examples/user_guide/Deploy_and_Export.ipynb

@@ -217,6 +217,8 @@
     "\n",
     "To turn a notebook into a deployable app simply append ``.servable()`` to one or more Panel objects, which will add the app to Bokeh's ``curdoc``, ensuring it can be discovered by Bokeh server on deployment. In this way it is trivial to build dashboards that can be used interactively in a notebook and then seamlessly deployed on Bokeh server.\n",
     "\n",
+    "When called on a notebook, `panel serve` first converts it to a python script using [`nbconvert.PythonExporter()`](https://nbconvert.readthedocs.io/en/stable/api/exporters.html), albeit with [IPython magics](https://ipython.readthedocs.io/en/stable/interactive/magics.html) stripped out. This means that non-code cells, such as raw cells, are entirely handled by `nbconvert` and [may modify the served app](https://nbsphinx.readthedocs.io/en/latest/raw-cells.html).\n",
+    "\n",
     "### Accessing session state\n",
     "\n",
     "Whenever a Panel app is being served the ``panel.state`` object exposes some of the internal Bokeh server components to a user.\n",