Comment .XML file content from ruby code

Can anyone tell me how can I comment following line on my .XML file by using ruby code.

I hope this can be done by using "nokogiri". but I'm just new to the ruby. any help would be much appreciated.

<message group="1" sub_group="1" type="none" destination="mydata" remark="mylist" userOnly="true "/>

output should be:

<!-- <message group="1" sub_group="1" type="none" destination="mydata" remark="mylist" userOnly="true "/> -->