docs: Add Docker usage instructions to README

Add section explaining how to run the project with Docker Compose,
including examples for different Ruby versions and development server.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: toshimaru

README.md

@@ -24,6 +24,26 @@ There are some enhancements in addition to SEO.
 - [ ] Comment System
 - [ ] etc. (see. https://github.com/railsdoc/railsdoc.github.io/issues)
 
-## Feature Request  
+## Docker Usage
+
+You can run this project using Docker Compose:
+
+```bash
+# Run the application
+docker compose run --rm app bundle exec rake
+
+# Run with a specific Ruby version
+RUBY_VERSION=3.3 docker compose run --rm app bundle exec rake
+
+# Run Jekyll server for development
+docker compose run --rm --service-ports app bundle exec jekyll serve --host 0.0.0.0
+```
+
+The Docker setup uses the official Ruby image and includes:
+- Ruby with YJIT enabled for better performance
+- Automatic bundle installation
+- Volume mounting for live development
+
+## Feature Request
 
 Please create an [issue](https://github.com/railsdoc/railsdoc.github.io/issues).