Automatic msg on acceptance of friend request

I would like to send an automatic message as soon as someone sends me a friend request and i accept it. For example. If you send me a request to add me to your friends list, on my acceptance of the request, a message like " hi there, thanks for adding me" should be automatically sent to requestor. How do i implement this? I also have neutron installed. Any suggestions?

In other words, i want to auto accept any subscriptions to the bot and send a welcome message