Jupyter docker stacks with a custom user

Jupyter allows to set a custom user instead of**_jovyan_** which is the default for all containers of the [Jupyter Docker Stack][1]. You need to change this user or its UID and GID in order to get the permissions right when you mount a volume from the host into the Jupyter container. The following steps are required: Create an unprivileged user and an asociated group on the host. Here we call the user and the group docker_worker Add your host user to the group.