Complete dataset description spreadsheet

[pablomendes]

We need to double check everything is correct, find empty/missing information and complete the spreadsheet before exporting it in LaTeX.

https://docs.google.com/spreadsheets/d/19KhVh5OMGJa7bO8sRrmBbBf9pM1e4g2CmvkcCdjcWKY/edit#gid=0