Add Folium reference notebook (#2672)

* add Folium reference

* clean up notebook

* Fix typo

* clear notebook

examples/reference/panes/Folium.ipynb

@@ -0,0 +1,79 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "source": [
+    "import folium\n",
+    "import panel as pn\n",
+    "\n",
+    "pn.extension(sizing_mode=\"stretch_width\")"
+   ],
+   "outputs": [],
+   "metadata": {}
+  },
+  {
+   "cell_type": "markdown",
+   "source": [
+    "The ``Folium`` pane renders [folium](http://python-visualization.github.io/folium/) interactive maps.\n",
+    "\n",
+    "#### Parameters:\n",
+    "\n",
+    "For layout and styling related parameters see the [customization user guide](../../user_guide/Customization.ipynb).\n",
+    "\n",
+    "* **``object``** (object): The Folium object being displayed\n",
+    "___"
+   ],
+   "metadata": {}
+  },
+  {
+   "cell_type": "markdown",
+   "source": [
+    "The `Folium` pane uses the built-in HTML representation provided by `folium` to render the map:"
+   ],
+   "metadata": {}
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "source": [
+    "m = folium.Map(location=[52.51, 13.39], zoom_start=12)\n",
+    "\n",
+    "folium_pane = pn.pane.plot.Folium(m, height=400)\n",
+    "\n",
+    "folium_pane"
+   ],
+   "outputs": [],
+   "metadata": {}
+  },
+  {
+   "cell_type": "markdown",
+   "source": [
+    "Like any other pane, the `Folium` pane's view can be updated by setting the `object` parameter:"
+   ],
+   "metadata": {}
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "source": [
+    "# Add a marker to the map\n",
+    "folium.Marker(\n",
+    "    [52.516, 13.381], popup=\"<i>Brandenburg Gate</i>\", tooltip=\"Click me!\"\n",
+    ").add_to(m)\n",
+    "\n",
+    "folium_pane.object = m"
+   ],
+   "outputs": [],
+   "metadata": {}
+  }
+ ],
+ "metadata": {
+  "language_info": {
+   "name": "python",
+   "pygments_lexer": "ipython3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}