include docs for standard lib

It took me ages to find documentation on the ocaml standard li. I think it would make sense to include it on the site.
Im happy to help out if you think its a good idea.

Start by reviewing the existing site structure and documentation to determine how standard-library material is currently represented and what “include it” would cover. The work is done when the agreed OCaml standard-library documentation is available on the site, but the issue does not identify files, tests, or a narrower scope.

Written by the indexing model from the issue text.