Diátaxis: Where are we?

[encukou]

There seems to be general consensus that diátaxis is a great theoretical model for structuring documentation. However, using it – restructuring Python's docs – is a monumental task that needs some planning upfront. @AA-Turner mentioned on the recent meeting that it would be good to start by charting the starting point: where on the Diátaxis chart do individual sections of the docs fall? With that info we should be able to start planning where they should fall, and restructure/rewrite accordingly.