docs: point root README at the site, profile, and deploy runbook (#2)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lesnik512

README.md

@@ -1 +1,17 @@
-# .github
+# .github
+
+Organization-level configuration and the public website for the
+[Modern Python](https://github.com/modern-python) GitHub organization.
+
+- **Website:** [modern-python.org](https://modern-python.org) — built from `docs/`
+  with MkDocs + Material and deployed to GitHub Pages via
+  [`.github/workflows/deploy.yml`](.github/workflows/deploy.yml) on every push to `main`.
+- **Org profile:** [`profile/README.md`](profile/README.md) renders on the
+  organization's GitHub landing page.
+- **Deployment & domain setup:** see [`docs/DEPLOYMENT.md`](docs/DEPLOYMENT.md).
+
+## Local development
+
+```bash
+uv run mkdocs serve
+```