Automate and document data update process

[Bisaloo]

It would be good to add a data-raw/ folder with a script to update the data provided in this package from the source google spreadsheet.

This would allow us to make sure the update process is always done in the same fashion, and thus simplify the code in a couple of places, such as:

https://github.com/epiverse-trace/epiparameter/blob/9524e66c9f2666dafd0b04bfe4d5b6f5febc122e/R/epidist.R#L68-L74

If we are sure this step is always run to update the bundled dataset, then there's no need to run it each time the function is called.

[Bisaloo]

Reference: https://r-pkgs.org/data.html#sec-data-data-raw