Kamon with Akka Documentation rewrote

Kamon Team, I've rewritten again kamon akka documentation from the first version in order to make it more coherent and a guide to follow if you want to add kamon to your akka project. Also, I've used tracing example and put a new version in kamon-examples folder called kamon-akka-example. This change will help new comers to akka in order to add kamon.

Thanks,

Sergio