Tooltip demo: Mention the option used in the track demo

Author: jzaefferer

demos/tooltip/tracking.html

@@ -36,7 +36,7 @@
 <p>Hover the field to see the tooltip.</p>
 
 <div class="demo-description">
-<p>Here the tooltips are positioned relative to the mouse, and follow the mouse while it moves above the element.</p>
+<p>Here the tooltips are positioned relative to the mouse, and follow the mouse while it moves above the element, using the <code>track</code> option.</p>
 </div>
 </body>
 </html>