[scroll-animations-1] Add issue mentioning that use cases need to be updated

Author: birtles

scroll-animations-1/Overview.bs

@@ -96,6 +96,7 @@ Note: Based on this <a
 href="https://github.com/w3c/csswg-drafts/blob/master/scroll-animations-1/Use%20cases.md">curated
 list of use cases</a>.
 
+Issue(4354): These use cases need updating.
 
 ## Scrollable picture-story show ## {#scrollable-animation-usecase}