Clarify contracts for writers and readers

[asinghvi17]

In general, users can expect writers (GeoJSON.write, Shapefile.write, GeoParquet.write, GeoDataFrames.write, etc) to accept either feature collections or table-like objects, as *.write(filename, obj). This is not always clear in the READMEs or package docs/docstrings.

This should be clarified in every README for these packages and in the docs as well, if those exist.

Similarly, readers should return a table-like object, possibly a feature collection. At least it should have some metadata. DataAPI.metadata functions should be included so we can propagate crs and geometry column info through e.g. DataFrame(GeoJSON.read(...)).

This is a good first issue to solve since it's mostly documentation modification!

[rafaqz]

I think making them all as much as possible identical is really important too. Like the same keywords, args etc wherever we can.

Even the docs should be basically the same text for the same functionality.