Dockerized Manager.io

Hi!

I have created yet another dockerized version of Manager.io.

I am using gitlab and gitlab-ci to automatically bump new releases when they become available. Images are tagged with the same manager.io release number.

I have implemented good practices related to data volumes and also permissions, as the container runs as non-priviledged.

You can find it here: https://hub.docker.com/r/privazio/managerio