[css-color-6][editorial] Add color-layers() to changes from level 5

Author: svgeesus

css-color-6/Overview.bs

@@ -515,6 +515,8 @@ Changes {#changes}
 
 		The new ''contrast-color()'' function allows one of a list of colors to be chosen,
 		based on the WCAG 2.1 contrast with a specified color.
+		The new ''color-layers()'' function returns the result of compositing
+		two or more colors, using a given blend mode.
 
 
 <wpt hidden title="older tests, not relevant for this level">