Update notebook example

notebooks/leafmap.ipynb

@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": null,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -19,6 +19,10 @@
     "    style=\"liberty\", projection=\"globe\", sidebar_visible=True, height=\"750px\"\n",
     ")\n",
     "m.add_basemap(\"USGS.Imagery\")\n",
+    "cities = (\n",
+    "    \"https://github.com/opengeos/datasets/releases/download/world/world_cities.geojson\"\n",
+    ")\n",
+    "m.add_geojson(cities, name=\"Cities\")\n",
     "m"
    ]
   }