Update ReadTheDocs page

[mjherzog]

The AboutCode pages on ReadTheDocs are outdated and due for a refresh. The major changes to make are:

• Update the main page based on changes outlined in:
  AboutCode-RTD-changes-22.03.04.docx
• Archive the GSoC and GSoD pages and remove them from the TOC and index because we have decided to use the GitHub wikis for our participation in those programs. We may want to move some of this content to the GH wikis - TBD.

[AyanSinhaMahapatra]

This is completed, see https://aboutcode.readthedocs.io/en/latest/index.html