Add some comments

Adding some comments testing my understanding of how this all works. Specific questions are marked with @sqs.

Btw, feature idea: it'd be really nice if I could just add a question on a specific function or line of code, so I didn't have to go through this routine
see https://github.com/sourcegraph/srclib-javascript/pull/4/files#r17695658 - passes IIRC was jsut from tern