add archival message to README.md

[zzstoatzz]

Closes

Example

Screenshots

Checklist

• [ ] References any related issue by including "Closes #" or "Closes ".
  • If no issue exists and your change is not a small fix, please create an issue first.
• [ ] Includes tests or only affects documentation.
• [ ] Passes pre-commit checks.
  • Run pre-commit install && pre-commit run --all locally for formatting and linting.
• [ ] Includes screenshots of documentation updates.
  • Run mkdocs serve view documentation locally.