fix: address remaining widget review feedback

apps/docs/docs/widgets/timetable/index.mdx

@@ -34,3 +34,5 @@ import streetDepartures from "./img/street-departures.png";
 ### Configuration
 
 <WidgetConfig configuration={timetableWidget.configuration} />
+
+For security, new or changed custom base URLs must resolve to a public IP address. Private and local hosts are rejected.