[css-color-5] Summarise what color-contrast() does in the intro paragraph

Author: svgeesus

css-color-5/Overview.bs

@@ -753,6 +753,10 @@ Selecting the most contrasting color: the ''color-contrast()'' function {#colorc
 	(typically a background, but not necessarily),
 	secondly, a list of two or more colors,
 	and thirdly, an optional target <a href="https://www.w3.org/TR/WCAG21/#contrast-minimum">luminance contrast</a> [[!WCAG21]].
+	It <a href="#winner">returns</a> the first color in the list
+	to meet or exceed the specified target contrast
+	or, if no target is given,
+	the color in the list with the greatest contrast.
 
 	The single color is separated from the list
 	with the keyword <css>vs</css>