Update documentation

### Feature Description

Update documentation, including but not limited to, the [README.md](https://github.com/CouncilDataProject/cdp-scrapers/blob/main/README.md) files. May also involve updating the [doc build system](https://github.com/CouncilDataProject/cdp-scrapers/tree/main/docs).

### Use Case

- Help instance maintainers in deployment.
- Help contributors.
- Improve collaboration and inter-operation within [the CouncilDataProject](https://github.com/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](https://github.com/CouncilDataProject/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`](https://github.com/CouncilDataProject/cdp-scrapers/blob/main/cdp_scrapers/scraper_utils.py#L429) and [`LegistarScraper`](https://github.com/CouncilDataProject/cdp-scrapers/blob/main/cdp_scrapers/legistar_utils.py#L378).
- Useful information for contributors.

### Depends

- [ ] #59
- [x] #89
- [ ] #95

Start with README.md and the docs build system, then review scraper_utils.py and legistar_utils.py, including IngestionModelScraper and LegistarScraper. Map the documentation needed for instance maintainers, CDP internal use, deployment, contributors, utility functions, and scraper derivation. Done means these use cases and concepts are documented across the relevant README and docs files.

Written by the indexing model from the issue text.