[css-color] Put warning in the code, too.

Author: tabatkins

css-color/Overview.bs

@@ -3297,6 +3297,8 @@ Adding New Color Classes</h4>
 			"hsl": function(hsv) {
 				return hsv.toHSL().toString("hsl");
 			}
+			/* Don't define an "hsv" stringifier type,
+			   because CSS won't understand it. */
 		}
 		</pre>
 

css-color/Overview.html

@@ -3404,6 +3404,8 @@ <h4 class="heading settled heading" data-level=15.5.2 id=api-adding-classes><spa
   "hsl": function(hsv) {
     return hsv.toHSL().toString("hsl");
   }
+  /* Don’t define an "hsv" stringifier type,
+     because CSS won’t understand it. */
 }
 </pre>