Combine GitHub-related pages

I don't think there's any reason to have these as separate pages:

- https://assemblyline.suffolklitlab.org/docs/authoring/github
- https://assemblyline.suffolklitlab.org/docs/authoring/weaver/publishing_and_github

A single GitHub page would make it easier for people to find the information they were looking for. I would locate it directly under Authoring interviews.