Tutorial - Setup a Phoenix application with Docker?

The ["PETE" stack](https://github.com/dwyl/technology-stack) is using some languages/framework that evolve rapidly (ex: elm 0.18 to 0.19 recently, see also the list of the release versions for Phoenix https://github.com/phoenixframework/phoenix/releases).

Making sure that all the versions are up to date or at least that the dev team is running projects with the same versions is time consuming. For example on each new project I have to go back and read again the installation page for Phoenix (https://hexdocs.pm/phoenix/installation.html) to make sure that everything is setup properly.

I think Docker can help us to reduce the setup time for new projects but most importantly it can make sure that all the team is running exactly the same stack and data (especially making sure that Postgres contains the same data for everyone)

Goal: Create a guide which explain how to setup a "PETE" application with Docker that we can reuse each time a new project is started