add demo gif (#4)

Author: PyAgni

README.md

@@ -83,8 +83,7 @@ I built this because I needed to feed my Apple Notes to LLMs while working on an
 
 ## In Action
 
-<!-- TODO: Add demo GIF or screenshot -->
-<!-- ![Demo](https://github.com/PyAgni/apple-notes-syncer/raw/main/assets/demo.gif) -->
+![Demo](./assets/demo.gif)
 
 Example output for a single note: