[css-cascade-3] Forgot to mention initial keyword, which was not part of CSS2 either.

Author: fantasai

css-cascade-3/Overview.bs

@@ -1059,6 +1059,7 @@ Additions Since Level 2</h3>
 
 	<ul>
 		<li>The 'all' shorthand
+		<li>The ''initial'' keyword
 		<li>The ''unset'' keyword
 		<li>Incorporation of animations and transitions into the <a>cascade</a>.
 	</ul>