Improve Documentation #140
Description
We have RTD set up minimally by #138, just using the README docs for now.
It would be nice to have improved documentation here:
- more complete and detailed API docs
- some tutorials with use cases (indexing packages from a list of PURLs, matching with scancode.io etc)
- reference docs (see https://github.com/nexB/aboutcode/wiki/GSOD-2023#add-reference-documentation-and-getting-started-guides-for-purldb for reference)