Reflect OpenWiki quickstart source shape

[HwangJohn]

Summary

Reflects the OpenWiki quickstart.md source shape in the existing llmwiki-docs pages.

• Updates the Knowledge Source format contract to describe openwiki/ nested source roots and quickstart.md as an OpenWiki index entrypoint.
• Keeps the wording constrained to OpenWiki source roots so a generic nested guide/quickstart.md is not described as a native hub.
• Updates quickstart graph choices so users can point llmwiki-serve at a repo root containing openwiki/quickstart.md or at the openwiki/ folder directly.
• Updates examples graph options with the same OpenWiki-generated repository docs shape.

Related implementation

Pairs with knowledge-bridge-labs/llmwiki-serve#7, which implements the parser/adapter behavior.

Validation

• npm ci
• npm run build
• npm run licenses:check
• npm run check