Update app.py

Add notification for model download

app.py

@@ -90,6 +90,11 @@ def server(input, output, session):
         model_path = Path("/code/models") / input.model()
 
         if not model_path.exists():
+            ui.notification_show(
+                f"Downloading model {input.model()}...",
+                type="message",
+                duration=3,
+            )
             hf_download(
                 model_name="quickmt/" + input.model(),
                 output_dir=Path("/code/models") / input.model(),