Container wrapper: documentation on how to update

[rogerkuou]

Instead of using the post.sh script as documented in https://github.com/CSCfi/hpc-container-wrapper, one can also install python dependencies with pip command through a Jupyter session. When testing on 2024-07-30, if the slurm job is killed then the same container is restarted, the installed dependency still exists.

We should investigate if there are too many legacy container started by each slurm job. And add suggestions to documentation.