add usa-airports-net.ipynb example to /notebooks (#49)

notebooks/usa-airports-net.ipynb

@@ -0,0 +1,44 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "source": [
+    "# USA Airports .NET Interactive Notebook 📓"
+   ],
+   "metadata": {}
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "source": [
+    "using System.Net.Http;\r\n",
+    "var dataUrl = \"https://raw.githubusercontent.com/RandomFractals/vscode-leaflet/main/data/geojson/usa-airports.geojson\";\r\n",
+    "var data = await new HttpClient().GetStringAsync(dataUrl);\r\n",
+    "data"
+   ],
+   "outputs": [],
+   "metadata": {
+    "dotnet_interactive": {
+     "language": "csharp"
+    }
+   }
+  }
+ ],
+ "metadata": {
+  "orig_nbformat": 4,
+  "language_info": {
+   "file_extension": ".cs",
+   "mimetype": "text/x-csharp",
+   "name": "C#",
+   "pygments_lexer": "csharp",
+   "version": "9.0"
+  },
+  "kernelspec": {
+   "display_name": ".NET (C#)",
+   "language": "C#",
+   "name": ".net-csharp"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 2
+}