distribution: optimise crates.io + docs.rs + GitHub discoverability

[sebastienrousseau]

Deliverables

• Update Cargo.toml keywords to include rust, markdown, jamstack, edge (replace generic cli)
• Add a comparison feature matrix (SSG vs Hugo vs Zola vs Astro) to README — devs decide in 30s on docs.rs
• Add GitHub topic tags: static-site-generator, rust, markdown, seo, accessibility, jamstack
• Submit 'Run a Rust SSG in your browser' Wasm demo as a Show HN
• Submit the benchmark report to This Week in Rust
• Create a CHANGELOG.md following Keep a Changelog format