fix: Add config.yml support for Docker deployment

Mount config.yml into Docker container and provide example template.

Changes:
- Mount config.yml as read-only volume in docker-compose.yml
- Create config.example.yml template for users
- Add config.yml to .gitignore (contains sensitive settings)
- Update README.md with config file setup instructions

Fixes 'Config file not found' error in Docker deployment.

Users should:
1. Copy config.example.yml to config.yml
2. Edit config.yml with their settings
3. Run docker compose up -d

docker-compose.yml

@@ -22,6 +22,7 @@ services:
     volumes:
       - guardden_data:/app/data
       - guardden_logs:/app/logs
+      - ./config.yml:/app/config.yml:ro
     networks:
       - guardden
     healthcheck: