Clarify that role="button" is required for dismiss-on-next-click popovers

Refs #15947

docs/_includes/js/popovers.html

@@ -123,7 +123,7 @@ sagittis lacus vel augue laoreet rutrum faucibus.">
   <p>Use the <code>focus</code> trigger to dismiss popovers on the next click that the user makes.</p>
   <div class="bs-callout bs-callout-danger" id="callout-popover-dismiss-click">
     <h4>Specific markup required for dismiss-on-next-click</h4>
-    <p>For proper cross-browser and cross-platform behavior, you must use the <code>&lt;a&gt;</code> tag, <i>not</i> the <code>&lt;button&gt;</code> tag, and you also must include a <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#tabindex"><code>tabindex</code></a> attribute.</p>
+    <p>For proper cross-browser and cross-platform behavior, you must use the <code>&lt;a&gt;</code> tag, <i>not</i> the <code>&lt;button&gt;</code> tag, and you also must include the <code>role="button"</code> and <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#tabindex"><code>tabindex</code></a> attributes.</p>
   </div>
   <div class="bs-example bs-example-padded-bottom">
     <a tabindex="0" class="btn btn-lg btn-danger bs-docs-popover" role="button" data-toggle="popover" data-trigger="focus" title="Dismissible popover" data-content="And here's some amazing content. It's very engaging. Right?">Dismissible popover</a>