📝 Document how/why to shell into a C-PAC container

[shnizzedy]

Related problem

Non-experts sometimes want to try some small step without installing [AFNI | FSL | whatever], and C-PAC can facilitate this, but that's not clear by the documentation.

Proposed feature

Add a page or section describing how to docker --rm -it --user $(id -u):$(id -g) --entrypoint /bin/bash / apptainer shell / singularity shell / cpac shell / cpac enter

Acceptance criteria

User or developer docs explain how to use a C-PAC image to work in a container in a shell

Alternatives

No response

Additional context

No response