Add description about function as contents (#33)

index.html

@@ -187,7 +187,7 @@ <h4>offsetX, offsetY</h4>
         </style>
         <div class="sample-explanation">
           <h4>contents</h4>
-          <p>Option <var>contents</var> is the plain text or HTML content of the balloon and can be a string or jQuery object. Set the <var>html</var> option to true if <var>contents</var> is a jQuery object or a string containing markup. If an img element has both title and alt property, use title.</p>
+          <p>Option <var>contents</var> is the plain text, HTML text, jQuery object or function. Set the <var>html</var> option to true if <var>contents</var> is a jQuery object or a string containing markup. Pass function which returns contents to update contents dynamically.</p>
           <code class="sample-script">
             $('.sample4-1').balloon({<br>
             &nbsp;&nbsp;html: true,<br>