[css-ui-4] Be more descriptive of the pointer cursor

Closes #1936

Author: frivoal

css-ui-4/Overview.bs

@@ -1294,6 +1294,7 @@ Values have the following meanings:
 
 		<dt style="cursor:pointer"><dfn>pointer</dfn>
 		<dd>The cursor is a pointer that indicates a link.
+		Often rendered as the backside of a hand with the index finger extended.
 
 		<dt style="cursor:progress"><dfn>progress</dfn>
 		<dd>