[css-contain-2] Mark informative text as such

Author: frivoal

css-contain-2/Overview.bs

@@ -1728,7 +1728,7 @@ the rendering state changes and the element either becomes or stops being
 
 This event is dispatched by posting a task at the time when the state change occurs.
 
-Note that elements in ''content-visibility: auto'' subtrees remain semantically
+Note: elements in ''content-visibility: auto'' subtrees remain semantically
 relevant even for elements that [=skip its contents=]. This means that it is
 inappropriate to use this signal to indefinitely skip DOM updates in the
 subtree that is skipped. Instead, it should be used to deprioritize updates,