Add device-cmyk() to changes.

Author: tabatkins

css-color/Overview.bs

@@ -4093,5 +4093,7 @@ Changes from Colors 3</h3>
 
 		<li>''color()'' function, for manipulating colors.
 
+		<li>''device-cmyk()'' function, for specifying colors in an output-device-specific CMYK colorspace.
+
 		<li>Addition of named color ''rebeccapurple''.
 	</ol>