Update readme.md with overview sheet information

[emquardokus]

Would be useful to update the readme.md to contain the overview sheet describing the assets, file types in this repo and how to use. Refer to paper.

[cmungall]

Yes!! The README is very minimal

It should link to
https://www.nature.com/articles/s41597-023-02018-0

Ideally all the CSVs would have a data dictionary