docs: methodology

[Akuukis]

Great stuff! I wish I could use it for my dashboard Pandemic Estimator but for that your data lacks documentation on methodology. I'm using JHU directly and I know what chaos it is, the most blatant example being that they provide "cumulative data" that's not cumulative quite often in practice. And the whole change of file formats, etc.

Can you please describe methodology how you deal with it? What has been omitted, what has been "adjusted" and how? Thank you!