Document usage with opam + npm #717
Description
As these bindings are now targeting Melange, the main supported workflow will be consuming it through opam. This means users of reason-react will need to add react as a dependency on their package.json manually. Similarly to how OCaml native bindings do with underlying dependencies.
This should be documented in the README and docs, including the version of ReactJS that is supported (I think 16 at the moment).