Mounting /etc/passwd is not always required

[jpetitcolas]

Not sure it is required everywhere. That was the case with PSQL, which executes a script requiring some valid users. But for file permissions, it should be fine without it.

https://github.com/marmelab/renard/blob/master/docker/Usage.md

To be checked.

[djhi]

We should also probably add a docker installation section somewhere and mention user namespaces: https://docs.docker.com/engine/security/security/