Update documentation

[dphoria]

Feature Description

Update documentation, including but not limited to, the README.md files. May also involve updating the doc build system.

Use Case

• Help instance maintainers in deployment.
• Help contributors.
• Improve collaboration and inter-operation within the CouncilDataProject.

Solution

Some of the concepts and information the documentation should explain and convey are (at the time of writing this feature request):

• Quickstart guide for instance maintainers.
• Quickstart guide for CDP internal use, e.g. from cdp-backend perspective.
• How this repository/package fits in the project, e.g. during instance deployment.
• Utility functions available in scraper_utils.py, legistar_utils.py.
• When/how to derive from IngestionModelScraper and LegistarScraper.
• Useful information for contributors.

Depends

• Scrapers provide API to return specific information outside of get_events() #59
• Srape for Granicus-hosted videos in LegistarScraper #89
• Split scraper_utils.py, legistar_utils.py #95