DS-653: Update demo - icon use case docs

docs-site/src/pages/pattern-lab/_patterns/20-elements/icon/20-icon-use-case-custom-svg.twig

@@ -22,7 +22,7 @@
       </bolt-li>
       <bolt-li>If you choose a HTML usage:
         <bolt-ul>
-          <bolt-li>Add the element class <code>class="e-bolt-icon"</code> and relevant modifier classes, and add the attribute <code>aria-hidden="true"</code> to the <code>&lt;svg&gt;</code> HTML element. Then you can display the icon using the modified <code>&lt;svg&gt;</code> markup.</bolt-li>
+          <bolt-li>Add the element class <code>class="e-bolt-icon"</code> and relevant modifier classes, add the attribute <code>aria-hidden="true"</code> and the three key attributes (if they weren't provided by default): <code>enable-background="new 0 0 32 32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg" </code> to the <code>&lt;svg&gt;</code> HTML element. Then you can display the icon using the modified <code>&lt;svg&gt;</code> markup.</bolt-li>
         </bolt-ul>
       </bolt-li>
     </bolt-ol>