Add link to scientifica data paper

[tvercaut]

The README should point to https://doi.org/10.1038/s41597-021-01064-w

We should also include a cff file: https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files

[aaronkujawa]

Thanks, I included both.