[cs-cascade-5] Link to issue from changelog

Author: mirisuzanne

css-cascade-5/Overview.bs

@@ -1754,6 +1754,7 @@ Changes</h2>
 		(<a href="https://github.com/w3c/csswg-drafts/issues/5793">Issue 5793</a>)
 	* Switched the ordering of unlayered styles
 		from highest to lowest priority in the normal origins.
+		(<a href="https://github.com/w3c/csswg-drafts/issues/6284">Issue 6284</a>)
 
 <h3 id="additions-l4">
 Additions Since Level 4</h3>