Package tarball guide placeholder.

The authoritative shared guides ship on HexDocs:
[hexdocs.pm/rulestead](https://hexdocs.pm/rulestead)

Start the lifecycle story with
[Flag Lifecycle](https://hexdocs.pm/rulestead/flag-lifecycle.html).

Package-local readers usually want one of these next:

- [Getting Started](https://hexdocs.pm/rulestead/getting-started.html)
- [Evaluation](https://hexdocs.pm/rulestead/evaluation.html)
- [Testing](https://hexdocs.pm/rulestead/testing.html)

Monorepo guides (GitHub):
[github.com/szTheory/rulestead/tree/main/guides](https://github.com/szTheory/rulestead/tree/main/guides)