chore(data-device): document that the offer may need to be manually d…

…estroyed after leave

src/data_device_manager/data_device.rs

@@ -34,7 +34,8 @@ pub trait DataDeviceHandler: Sized {
     fn enter(&mut self, conn: &Connection, qh: &QueueHandle<Self>, data_device: &WlDataDevice);
 
     /// The drag and drop pointer has left the surface and the session ends.
-    /// The offer will be destroyed.
+    /// The offer will be destroyed unless it was previously dropped.
+    /// In the case of a dropped offer, the client must destroy it manually after it is finished.
     fn leave(&mut self, conn: &Connection, qh: &QueueHandle<Self>, data_device: &WlDataDevice);
 
     /// Drag and Drop motion.