Simplify the Docker setup

[julienrf]

While working on the blog article I noticed that many lines were unused.

I also figured out how to fix the links between the master and worker nodes.

[tarzanek]

I was hoping to have network isolation, so now everything is host network?

[tarzanek]

okay, so if we are going to merge it
we need to make sure docker is used only for demos

let's put

This approach is useful if you do not need a high-level of performance, and want to quickly try out the Migrator without having to set up a real cluster of nodes. It requires Docker and Git.

into a caution or note section

[julienrf]

Done in c2835e5.