[css-values-5] Added palette-mix() to list of mix notations

Author: svgeesus

css-values-5/Overview.bs

@@ -240,6 +240,8 @@ Mixing and Interpolation Notations: the *-mix() family</h2>
 		for interpolating two <<color>> values
 	* ''cross-fade()'',
 		for interpolating <<image>> values
+	* ''palette-mix()'',
+		for interpolating two 'font-palette' values
 
 	and finally the generic ''mix()'' notation,
 	which can represent the interpolation of any property's values