[css-background-4][editorial] Noted new values for background-clip in Changes section

Author: SebastianZ

css-backgrounds-4/Overview.bs

@@ -415,7 +415,7 @@ Additions since [[CSS3BG]]</h3>
 
 	* turned 'background-position' into a shorthand and added physical and logical longhands
 	* added logical keywords to <<bg-position>>
-	* added 'background-clip'
+	* added ''background-clip/border-area'' and ''background-clip/text'' values to 'background-clip'
 	* added 'background-tbd'
 	* added 'background-repeat-*' longhands