docs: reason-native async i/o and JSON patterns

[cdaringe]

Problem

There doesn't seem to be an idiomatic reference to how we do:

• async in reason
• JSON + types in reason

I've been learning ocaml, and figured I'd sprinkle in some reason given that they seem to interop fine w/ my dune builds 👍 , but have been largely relying on ocaml docs to help guide me on this topic(s).

Discussion

• I just wrote this forum response for recommending a JSON (de)serialization pattern. Is that the reason-way? Is there such thing as the reason-way?
  • RWO has a JSON section. It still seems relevant ish. It's a bit heavy handed, and probably not what I would recommend to users for pragmatic usage right off the bat?
• Is light weight threads (lwt) how we (recommended) do async in reason-native? If not, should there be parity w/ what the JS API looks like?

I'm happy to add to docs if ocaml & reason experienced users can help guide me. I've spent too much time trying to figure this out :).

I'm looking for a hypothetical "hands-on" section of the docs that says "let's call this API and parse the response" or let's read this file from disk and do XYZ with the streaming data.