chore(showcase): Add zatsuzen

[ryo4004]

Add my portfolio website Zatsuzen to sites.yml.

[DanielRuf]

Hi @ryo4004, please do not create PRs from your master branch but use a new branch in the future =)

[ryo4004]

@DanielRuf, Sorry for my lack experience, I'll be more careful.

[laurieontech]

Hey @ryo4004 I'm going to reopen this! You're welcome to make changes wherever you like in your personal repository.

@DanielRuf Thanks for your assistance with maintaining the project. Please refer to this document on triaging GitHub issues to follow project best practices.

[laurieontech]

Congrats @ryo4004! Your PR is merged!

[gatsbot]

Holy buckets, @ryo4004 — we just merged your PR to Gatsby! 💪💜

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