[css-writing-modes] Add defer proposal from ML as an issue <https://lists.w3.org/Archives/Public/www-style/2015Apr/0212.html>

Author: kojiishi

css-writing-modes/Overview.bs

@@ -2070,6 +2070,7 @@ Auto-sizing Block Containers in Orthogonal Flows</h4>
       the used 'column-count' follows from filling the resulting multi-column layout
       with the box's content.
   </ol>
+  <p class="issue"><a href="https://lists.w3.org/Archives/Public/www-style/2015Apr/0212.html">Defer proposal in ML</a></p>
 
   <p>
     The used <i>inline size</i> of the resulting multi-column element is then calculated: