add reference to issue #261 with note that there isn't consensus yet …

…on what cover can be

index.html

@@ -1770,6 +1770,9 @@ <h4>Cover</h4>
 					<p>The <dfn>cover</dfn> is a resource that user agents can use to present the <a>Web Publication</a>
 						(e.g., in a library or bookshelf, or when initially loading the Web Publication).</p>
 
+					<p class="issue" data-number="261">The working group has not reached consensus on whether the cover
+						should be any resource or should be limited to images.</p>
+
 					<section id="cover-infoset">
 						<h5>Infoset Requirements</h5>