add visibility note to docs about captions

docs/javascript.html

@@ -1530,6 +1530,7 @@ $('#myCollapsible').on('hidden', function () {
 
             <h3>Optional captions</h3>
             <p>Add captions to your slides easily with the <code>.carousel-caption</code> element within any <code>.item</code>. Place just about any optional HTML within there and it will be automatically aligned and formatted.</p>
+            <p><strong>Captions are hidden in mobile views</strong> and shown with viewports greater than 768px wide.</p>
             <div class="bs-docs-example">
               <div class="carousel slide bs-docs-carousel-example">
                 <ol class="carousel-indicators">