REQ: Display task time in notification

[bomberstudios]

It would be übercool if you displayed the time it took to run the task.

I use it in http://github.com/bomberstudios/fluby/blob/master/lib/fluby.rb#L163 and it's nice because you can use it as some sort of benchmark (compilation takes too long? something could be improved. compilation was too fast? it may not be working as expected...)

Thanks in advance : )