clarify support of select items (which is none) for input-prepend/append

docs/templates/pages/base-css.mustache

@@ -890,7 +890,7 @@
   <p>{{_i}}Adding on top of existing browser controls, Bootstrap includes other useful form components.{{/i}}</p>
 
   <h3>{{_i}}Prepended and appended inputs{{/i}}</h3>
-  <p>{{_i}}Add text or buttons before or after any text-based input.{{/i}}</p>
+  <p>{{_i}}Add text or buttons before or after any text-based input. Do note that <code>select</code> elements are not supported here.{{/i}}</p>
 
   <h4>{{_i}}Default options{{/i}}</h4>
   <p>{{_i}}Wrap a <code>.add-on</code> and an <code>input</code> with one of two classes to prepend or append text to an input.{{/i}}</p>