docs(datepicker): add note about format function

Author: Calamari

pug/page-contents/pickers_content.html

@@ -57,9 +57,9 @@ <h5>Options</h5>
               </tr>
               <tr>
                 <td>format</td>
-                <td>String</td>
+                <td>String || Function</td>
                 <td>'mmm dd, yyyy'</td>
-                <td>The date output format for the input field value.</td>
+                <td>The date output format for the input field value or a function taking the date and outputitng the formatted date string.</td>
               </tr>
               <tr>
                 <td>parse</td>