JsInfo documentation

I'm working on a ruleset for js_of_ocaml, which transpiles OCaml bytecode to javascript.

I'd like to have my rules emit JsInfo so they integrate well with rules_js. The comments in js_info.bzl are pretty sparse. Do you have any additional information about what I should put in JsInfo? In particular the sources attribute. My rules just emit js files, is it sufficient to put them in a depset and add them to sources?

What is the `transitive_sources` attribute for? Shouldn't transitive (i.e. indirect) deps be added via the `transitive` argument of depset()? Or is there some reason they need to be kept separate?

FWIW it's been a long time since I last did any js programming so I'm kinda flying blind.

Thanks,

Gregg

Read js_info.bzl, focusing on the sparse comments for JsInfo, sources, and transitive_sources. Clarify what files belong in sources and how transitive_sources differs from depset transitive dependencies; done when the file documents these semantics for rules authors.

Written by the indexing model from the issue text.