Data sources in Julia land

[asinghvi17]

A huge feature of GIS platforms is easy data access from providers like OpenStreetMap, WorldClim, weather records / forecasters, etc.

We should add a section on this to the book (even if it isn't quite in the other books so explicitly).

[Nowosad]

It exists in the geocompr book -- https://r.geocompx.org/read-write#geographic-data-packages