- check if socket group ID is presented in /etc/group
- if presented, just add 'docker' user to this group
- if not, create 'docker' group and add 'docker' user to this group
Fixes issue #20
Envsubst allows to use dynamic container name
We use image name env substitution with docker-compose and .env to select right image tag for local development
Within alpine, envsubst installed with gettext package.