Replace stale `cargo install sukr` with install-from-source.
Replace Step 4 dead-end with inline base.html, page.html,
and content/default.html templates. Add "View your site"
completion step. Improve Next Steps with reading-order context.
Self-documenting docs site built with sukr itself (dogfooding):
- docs/site.toml with sukr.io base URL
- docs-specific templates with sidebar navigation
- Dark theme CSS, responsive layout
- Documentation: getting-started, configuration, features
Also: improved error chaining for better template debugging
