[css-scroll-snap] Document that Safari makes start/end of scrollable area snappable automatically.

Author: tabatkins

css-scroll-snap/Overview.bs

@@ -400,7 +400,10 @@ Scroll Snapping Coordinates: the 'scroll-snap-points-x' and 'scroll-snap-points-
 	are not affected by 'scroll-snap-padding'/'scroll-snap-destination'.
 
 	Issue: Should we add <css>start-edge</css> and <css>end-edge</css> keywords here, so that the start and end of the scrollable area can be defined as reachable?
-	This would be good for e.g. maps. (See <a href="https://lists.w3.org/Archives/Public/www-style/2015Jul/0453.html">Matt Rakow's take</a> on not having <css>start</css> or <css>end</css> here.)
+	This would be good for e.g. maps.
+	(See <a href="https://lists.w3.org/Archives/Public/www-style/2015Jul/0453.html">Matt Rakow's take</a> on not having <css>start</css> or <css>end</css> here.)
+	Note, tho, that Safari adds start/end automatically
+	(<a href="https://www.webkit.org/blog/4017/scroll-snapping-with-css-snap-points/">document at end of their announcement post</a>).
 
 	Issue: It was <a href="https://lists.w3.org/Archives/Public/www-style/2015Jul/0453.html">suggested</a> that repeat() be mutually exclusive with element-based snap positions. Is there a better way to integrate this than having the initial value here be "elements"?