[css-will-change] Fix example.

Author: tabatkins

css-will-change/Overview.bs

@@ -52,7 +52,7 @@ Don't Spam 'will-change' Across Too Many Properties or Elements</h4>
 
 	A common initial response to seeing 'will-change' is to assume that code like this is a good idea:
 
-	<pre>* { will-change: all; }</pre>
+	<pre>* { will-change: transform, opacity /* , ... */; }</pre>
 
 	After all, this tells the browser to go ahead and optimize everything,
 	which has to be good right?