[css-fonts-5][editorial] add wpt

Author: svgeesus

css-fonts-5/Overview.bs

@@ -1169,6 +1169,7 @@ Changes
 	font-palette-remove.html
 	font-palette-vs-shorthand.html
 	font-palette.html
+	font-palette-values-relative-colors.html
 	font-shorthand-serialization-001.html
 	font-shorthand-serialization-font-stretch.html
 	font-shorthand-serialization-prevention.html