add comment in ModelView about tile_layer_url not being a URL

Author: TomGoBravo

flask_admin/contrib/geoa/view.py

@@ -5,5 +5,7 @@
 class ModelView(SQLAModelView):
     model_form_converter = form.AdminModelConverter
     column_type_formatters = typefmt.DEFAULT_FORMATTERS
+    # tile_layer_url is prefixed with '//' in flask_admin/static/admin/js/form.js
+    # Leave it as None or set it to a string starting with a hostname, NOT "http".
     tile_layer_url = None
     tile_layer_attribution = None