docs(readme): update directory structure to include skills folder

[tsubasaogawa]

Reflect the addition of the skills directory in the project layout description to keep documentation in sync with the codebase.

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.

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Description

Reflect the addition of the skills directory in the project layout description to keep documentation in sync with the codebase.

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Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• New collection file.
• New skill file.
• Update to existing instruction, prompt, chat mode, collection or skill.
• Other (please specify): Fix readme

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Additional Notes

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull request overview

This PR updates the README.md to document the skills/ directory in the project structure section, ensuring the documentation reflects the actual repository contents.

Changes:

• Added skills/ directory entry to the repository structure diagram
• Updated tree structure symbols to correctly show skills/ as the last item