Updating README

[Yannik]

Hi,

I think the README could use a few updates:

• using the docker ansible_connection removes any need for ssh, (apart from the readme: IMO this should be used by default). this also removes any need for the whole custom routing part on mac os x.
• actually, the service module does already work atleast with the minimal sysvinit-utils debian:jessie ships with. I would assume that this is also the case for ubuntu:16.04, but this will need verification.
• additional documentation about the parameters the role accepts for a host should be added
• perhaps you'd like to link my role, from what I have seen, none of the other roles that are currently linked actually make use of separating services through different container types and linking these.
• the defaults should be documented (i.e. provision_docker_groups: ['docker_containers'] is really useful to know.)