#51 add some wording and ref for GeoJSON

Author: justb4

workshop/jupyter/content/notebooks/04-vector-data.ipynb

@@ -87,7 +87,8 @@
     "}\n",
     "```\n",
     "\n",
-    "GitHub for example is able to display [GeoJSON-encoded data on-the-fly](https://github.com/jachym/jrdata/blob/master/jsons/stops.geojson).\n",
+    "GitHub for example is able to display [GeoJSON-encoded data on-the-fly](https://github.com/jachym/jrdata/blob/master/jsons/stops.geojson). Note that coordinates are always in \"easting, northing\", thus longitude, latitude here. Note: the use of alternative coordinate reference systems was\n",
+    "removed from an earlier version of the [GeoJSON specification](https://datatracker.ietf.org/doc/html/rfc7946). However: \"*...where all involved parties have a prior arrangement, alternative coordinate reference systems can be used without risk of data being misinterpreted.*\"\n",
     "\n",
     "### Geography Markup Language (GML)\n",
     "\n",