Update checkpoints.mdx

Co-authored-by: ellipsis-dev[bot] <65095814+ellipsis-dev[bot]@users.noreply.github.com>

Author: hannesrudolph

docs/features/checkpoints.mdx

@@ -9,7 +9,7 @@ Checkpoints let you:
 - Revert to previous project states without losing work
 
 <div style={{ position: 'relative', paddingBottom: '56.25%', height: 0, overflow: 'hidden' }}>
-  <iframe
+  <iframe title="Checkpoints Tutorial Video"
     src="https://www.youtube.com/embed/Ho30nyY332E"
     style={{
       position: 'absolute',