Add explanation for Filtering Presence Changes in Documentation

Updated the documentation to provide instructions on how to filter out presence changes.

docs/devtools.mdx

@@ -72,7 +72,8 @@ Within the `Yorkie 🐾` panel, you will find the `History` panel at the top, th
 - Easily debug through time-travel and replay.
     - Move the slider and click on an event to check event details and see how the document has changed.
     - Convenient navigation is possible using the arrow buttons at the top right or using the directional keys.
-
+    - If you are only interested in document changes, click the `Y` button next to the navigation buttons to filter out presence changes, and toggle it again to undo.
+
 <video autoPlay loop muted playsInline style={{ maxWidth: '900px' }}>
     <source src="/assets/images/docs/devtools-history.mov"/>
 </video>