[css-color-5][editorial] link definition

Author: Chris Lilley

css-color-5/Overview.bs

@@ -31,6 +31,7 @@ spec:css-color-4; type:dfn; text:rectangular orthogonal color
 spec:css-color-4; type:dfn; text:cylindrical polar color
 spec:css-color-4; type:value; text:none
 spec:css-color-4; type:value; text:srgb
+spec:css-color-4; type:dfn; text:modern color syntax
 </pre>
 <link rel="stylesheet" href="style.css" />
 <style>