mention lack of support for split button dropdowns in vertical button groups

components.html

@@ -1103,7 +1103,7 @@ base_url: "../"
 {% endhighlight %}
 
     <h3 id="btn-groups-vertical">Vertical variation</h3>
-    <p>Make a set of buttons appear vertically stacked rather than horizontally.</p>
+    <p>Make a set of buttons appear vertically stacked rather than horizontally. <strong class="text-danger">Split button dropdowns are not supported here.</strong></p>
     <div class="bs-example">
       <div class="btn-group-vertical">
         <button type="button" class="btn btn-default">Button</button>