Docs - clarify purpose of CSS class .in to .fade

Author: tomkel

docs/_includes/js/tabs.html

@@ -81,7 +81,7 @@ <h3>Markup</h3>
 {% endhighlight %}
 
   <h3>Fade effect</h3>
-  <p>To make tabs fade in, add <code>.fade</code> to each <code>.tab-pane</code>. The first tab pane must also have <code>.in</code> to properly fade in initial content.</p>
+  <p>To make tabs fade in, add <code>.fade</code> to each <code>.tab-pane</code>. The first tab pane must also have <code>.in</code> to make the initial content visible.</p>
 {% highlight html %}
 <div class="tab-content">
   <div role="tabpanel" class="tab-pane fade in active" id="home">...</div>