[css-display] Add issue about box-suppress:hide details.

--HG--
extra : rebase_source : 9dccb21feca15d20e2aefaa0c3ca34f28f204a0e

Author: tabatkins

css-display/Overview.bs

@@ -415,6 +415,9 @@ Controlling box generation: the 'box-suppress' property</h2>
 			Properties that rely on boxes but do not rely on layout,
 			such as animations, 'counter-increment', etc.,
 			must work as normal on this element and its descendants.
+
+			Issue: This needs more clarity about what "layout-related" and "participates in layout" means.
+			Does the box still generate anonymous boxes, etc.?
 	</dl>
 
 	Issue: We welcome better naming suggestions on this property.