add markup with default iframe tab in docs

docs/javascript/iframe.md

@@ -27,6 +27,32 @@ To get the iframe 100% working you need the following content-wrapper markup:
 </div>
 ```
 
+###### Markup with Default IFrame Tab
+```html
+<div class="content-wrapper iframe-mode" data-widget="iframe" data-loading-screen="750">
+  <div class="nav navbar navbar-expand-lg navbar-white navbar-light border-bottom p-0">
+    <a class="nav-link bg-danger" href="#" data-widget="iframe-close">Close</a>
+    <a class="nav-link bg-light" href="#" data-widget="iframe-scrollleft"><i class="fas fa-angle-double-left"></i></a>
+    <ul class="navbar-nav" role="tablist">
+      <li class="nav-item active" role="presentation"><a class="nav-link active" data-toggle="row" id="tab-index" href="#panel-index" role="tab" aria-controls="panel-index" aria-selected="true">Dashboard v1</a></li>
+    </ul>
+    <a class="nav-link bg-light" href="#" data-widget="iframe-scrollright"><i class="fas fa-angle-double-right"></i></a>
+    <a class="nav-link bg-light" href="#" data-widget="iframe-fullscreen"><i class="fas fa-expand"></i></a>
+  </div>
+  <div class="tab-content">
+    <div class="tab-pane fade active show" id="panel-index" role="tabpanel" aria-labelledby="tab-index"><iframe src="./index.html" style="height: 671px;"></iframe></div>
+    <div class="tab-empty">
+      <h2 class="display-4">No tab selected!</h2>
+    </div>
+    <div class="tab-loading">
+      <div>
+        <h2 class="display-4">Tab is loading <i class="fa fa-sync fa-spin"></i></h2>
+      </div>
+    </div>
+  </div>
+</div>
+```
+
 ##### Usage
 This plugin can be activated as a jQuery plugin or using the data api.