[css-cascade-5] Link to layers/layer issue w3c#5855

Author: mirisuzanne

css-cascade-5/Overview.bs

@@ -1353,6 +1353,8 @@ Layer-Declaring Shorthand: the ''@layers'' rule</h3>
 
 	''@layers'' rules are allowed anywhere an empty ''@layer'' rule is allowed.
 
+	Issue(w3c/csswg-drafts#5855): Rename @layers to @layer
+
 <h3 id="preshint">
 Precedence of Non-CSS Presentational Hints</h3>