feat(M5): Final hardening, CI surface, and documentation closeout

README.md

@@ -169,3 +169,20 @@ Additional pi-specific guidance lives in [docs/PI.md](docs/PI.md).
 
 For development prerequisites, quality tooling, and the `pnpm run check`
 contract, see [docs/DEVELOPMENT.md](docs/DEVELOPMENT.md).
+
+## Contributing / Development
+
+See **[docs/DEVELOPMENT.md](docs/DEVELOPMENT.md)** for the full development guide.
+
+Quick reference — the single quality gate every contributor must pass:
+
+```bash
+pnpm install
+pnpm run check      # lint · typecheck · test · verify:pi · verify:reviewers · verify:docs · verify:generated
+```
+
+Prerequisites: Node.js 20+, pnpm 10+, `shellcheck` (brew / apt), `ripgrep` (brew / apt).
+
+CI runs the same `pnpm run check` command on both `ubuntu-latest` and `macos-latest`
+(see `.github/workflows/check.yml`).  External link checking runs separately on a
+weekly schedule (`.github/workflows/check-online.yml`).