Update app to show warning when metadata file is not found

app.py

@@ -136,7 +136,11 @@ def load_recording(basedir):
         "Enable HTML download", False, key="enable_html_download"
     )
     replay_file = replay_file.replace(".json", "")
-
+    
+    if not Path(basedir).joinpath('metadata.json').exists():
+        st.sidebar.error(f"Metadata file not found at {basedir}/metadata.json. This is likely an issue with Huggingface Spaces. Try cloning this repo and running locally.")
+        st.stop()
+    
     metadata = load_json_no_cache(basedir, "metadata")
 
     # convert timestamp to readable date string