tidy up and flag key notebooks

[stevehadd]

We have some key notebooks in the repository that show elements of what we have worked on from a data engineering, modelling, XAI, data exploration etc. perspective. We should create a wiki page that highlights the key notebooks some one looking the repo for the first time should look at, and tidy these notebooks up so they are easy to follow. This would be a good thing to do as part of tidying up for the end of the PRISM funded pohase of the project.

[stevehadd]

I have updated the readme to describe the contents of the data prep class. You might find this useful as an example of what I was thinking @hannahbrown7

[stevehadd]

I think we've done all the stuff around identifying the key notebooks. One thing we didn't think about was making the key artifacts saved to ML accessible centrally. I'm going to copy the models saved by Hannah and update the notebooks to point to the centrally stored version.