Update Tables in Documentation

[PaulWAyers]

We need to update the table in the landing page of the documentation, because NIST does not provide local properties but HCI does. (things are shifted over by one column at the bottom of the table).

I'm wondering how we can easily express which atoms/ions are covered by which datasets. It would be good to have a very short description of which species are covered in each dataset, especially since only the hci dataset is actively changing.