add warning if we reach the deprecated code path.

Author: toger5

src/ClientWidgetApi.ts

@@ -525,6 +525,10 @@ export class ClientWidgetApi extends EventEmitter {
             // For backwards compatibility we still call the deprecated
             // readRoomEvents and readStateEvents methods in case the client isn't
             // letting us know the currently viewed room via setViewedRoomId
+            console.warn(
+                "The widgetDriver uses deprecated behaviour:\n"+
+                "It does not set the viewedRoomId using `setViewedRoomId`"
+            );
             events = await (
                 // This returns [] with the current driver of Element Web.
                 // Add default implementations of the `readRoomEvents` and `readStateEvents`