Add missing namespace declaration to event example (#10351)

Author: AhmedAlaa4611

broadcasting.md

@@ -571,6 +571,8 @@ If you would like to broadcast your event using the `sync` queue instead of the
 ```php
 <?php
 
+namespace App\Events;
+
 use Illuminate\Contracts\Broadcasting\ShouldBroadcastNow;
 
 class OrderShipmentStatusUpdated implements ShouldBroadcastNow