Add brief READMEs where appropriate

[llewelld]

User story: "As someone replicating the results, I'd like to be able to check documentation, in order to be able to run the experiments as swiftly and straightforwardly as possible."

It would be helpful for future users of the repository if there were very brief instructions for how to use the slurm scripts to run the various experiments.

Most of these should be pretty simple, because it should just be a case of running the slurm sbatch script, or similar.