document HNSCC_data

[louisabraham]

@xyang23 Could you add some README in HNSCC_data to explain how that data is made?

[louisabraham]

@xyang23 the readme would have to be there: https://github.com/lasso-net/lassonet/tree/master/examples/data

[xyang23]

See Pull Request #24

[ilemhadri]

@xyang23 i just linked that pull request to this issue. This way, merging the former will close the latter.