Package should follow PEP561 and include py.typed

[christuart]

As I understand it, since this package is typed you can add an empty file to datafiles/ named py.typed and then projects which import the datafiles package will be able to make use of datafiles's type annotations in their own static analysis.

I could be wrong as I only discovered today that I should put this file into my packages, but this is what I understood from: https://peps.python.org/pep-0561/