Document that Tab show method is async

[skip sauce]

Author: cvrebert

docs/_includes/js/tabs.html

@@ -98,7 +98,7 @@ <h4><code>$().tab</code></h4>
   </p>
 
   <h4><code>.tab('show')</code></h4>
-  <p>Selects the given tab and shows its associated content. Any other tab that was previously selected becomes unselected and its associated content is hidden.</p>
+  <p>Selects the given tab and shows its associated content. Any other tab that was previously selected becomes unselected and its associated content is hidden. <strong>Returns to the caller before the tab pane has actually been shown</strong> (i.e. before the <code>shown.bs.tab</code> event occurs).</p>
   {% highlight js %}$('#someTab').tab('show'){% endhighlight %}
 
   <h3 id="tabs-events">Events</h3>