Replace JSON config with .env files

- Add python-dotenv dependency for environment variable loading
- Replace params.json and params-local.json with .env files
- Add --local and --local-stacosys flags to makesite.py
- Update Makefile to auto-detect stacosys availability
- Document configuration and usage in README.md

README.md

@@ -7,3 +7,38 @@ This static blog generator code is under MIT license.
 
 "Blog du Yax" content is under [CC-BY-NC-SA](https://creativecommons.org/licenses/by-nc-sa/3.0)
 
+## Configuration
+
+Configuration is managed through `.env` files:
+
+| File | Description |
+|------|-------------|
+| `.env` | Production configuration |
+| `.env.local` | Local development (no Stacosys) |
+| `.env.local-stacosys` | Local development with local Stacosys |
+
+Environment variables:
+
+- `TITLE` - Site title
+- `SUBTITLE` - Site subtitle
+- `AUTHOR` - Author name
+- `SITE_URL` - Base URL for the site
+- `STACOSYS_URL` - Stacosys API endpoint (optional)
+- `EXTERNAL_CHECK` - Script for git change detection
+
+## Usage
+
+```bash
+# Production build (uses .env)
+uv run python makesite.py
+
+# Local development without Stacosys (uses .env.local)
+uv run python makesite.py --local
+
+# Local development with local Stacosys (uses .env.local-stacosys)
+uv run python makesite.py --local-stacosys
+
+# Or use make for local development
+make site
+```
+