Add docs about loading the ipywidgets extension

examples/reference/panes/IPyWidget.ipynb

@@ -17,7 +17,13 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "The ``IPyWidget`` pane renders any ipywidgets model both in the notebook and in a deployed server. This makes it possible to leverage this growing ecosystem directly from within Panel simply by wrapping the component in a Pane or Panel.\n",
+    "The ``IPyWidget`` pane renders any ipywidgets model both in the notebook and in a deployed server. This makes it possible to leverage this growing ecosystem directly from within Panel simply by wrapping the component in a Pane or Panel. However when rendering ipywidgets on the server you may have to initialize the `ipywidgets` extension by running:\n",
+    "\n",
+    "```python\n",
+    "pn.extension('ipywidgets')\n",
+    "```\n",
+    "\n",
+    "In the notebook this is not necessary since Panel simply uses the regular notebook ipywidget renderer. Particularly in JupyterLab importing the ipywidgets extension in this way may interfere with the UI and render the JupyterLab UI unusable, so enable the extension with care.\n",
     "\n",
     "#### Parameters:\n",
     "\n",