Follow the steps for Ubuntu here : https://docs.docker.com/engine/installation/linux/docker-ce/ubuntu/
The only change is on step for you should change $(lsb_release -cs) to xenial.
This is because $(lsb_release -cs) returns the name of the distro, in this case would be loki, and since docker-ce does not have packages ment for loki we have to manually input the unbuntu distro it was based on.