Add open attribute to the dialog element example

Author: ericwbailey

partials/section.interactive.hbs

@@ -17,7 +17,10 @@
 
   <!-- Start of #subsection-dialog -->
   <h3 id="subsection-dialog">Dialog</h3>
-  <dialog id="dialog">
+  <dialog
+    open
+    id="dialog">
+    <h2>This is a dialog title</h2>
     <p>This is dialog content.</p>
     <button type="button">
       Close