Update readme.

README.md

@@ -7,6 +7,7 @@ The table displays data in a tabular format and offers rich support to radio, ch
 * [Documentation](http://wenzhixin.net.cn/p/bootstrap-table/docs/documentation.html)
 * [Examples](http://wenzhixin.net.cn/p/bootstrap-table/docs/examples.html)
 * [JSFiddle Examples](https://github.com/wenzhixin/bootstrap-table/blob/master/docs/jsfiddle-examples.md)
+* [Extensions](http://wenzhixin.net.cn/p/bootstrap-table/docs/extensions.html)
 
 
 ## LICENSE