ultra-short, illustrative story for patterns

Story provides a more narrative, less academic description to a pattern. When a pattern has a good narrative description at the first few sections, it helps people deciding quickly whether this is something they want to dive deeper. Some patterns provide good narrative while some other patterns lack those narrative angle. It would help to add story or improve narrative description to the patterns that don't have good narratives.

Issue にはファイルもテストも記載されていません。Repository の pattern ドキュメントを確認し、冒頭のセクションに簡潔な説明がないエントリを特定してください。選択した pattern に、読者がさらに調べるかどうかを判断するのに役立つ有用なストーリーがあれば完了です。