Changes to Docker and Podman documentation

[herzenschein]

This updates the container documentation to follow my findings under https://github.com/herzenschein/herz-podman/tree/main/writefreely.

There are a few noteworthy things here:

• The bash script wasn't needed and it was outdated
• The docs mention an example config file that doesn't exist yet (config/sample-config.ini), which should be added later
• This also adds instructions for Podman
• It has a troubleshooting section

I plan to add Podman Quadlets in the future, following the scheme I devised under https://github.com/herzenschein/herz-quadlet/tree/main/writefreely.

Companion pull request: https://github.com/writefreely/writefreely/pull/784

Counter pull request: https://github.com/writefreely/documentation/pull/39