Add docker container

[snowe2010]

Is this a fix or a feature?

• [ ] Bug fix
• [x] Feature
• [ ] Refactor

Describe the feature - fix - refactor:

• Update instructions, add asdf file for versions
• Get it running on docker
• Add .env to gitignore

How was this tested?

• [ ] open index.html
• [x] localhost
• [x] terminal

Where should the reviewer start - test:

You should be able to run docker-compose up -d and have postgres and shared milk backend start. You can then run docker-compose exec app bundle exec rake db:setup db:migrate and your migrations will run.

Then the server is accessible like normal.

Additional comments:

This is pre work to allow deploying this as a docker container on any platform.