📝 docs(README): add arichtman blog to showcase

[arichtman]

Summary

Added my website to the "using tabi" section

Related issue

None

Changes

Only README.md

Accessibility

No changes to website or CSS etc.

Screenshots

Type of change

• [ ] Bug fix (fixes an issue without altering functionality)
• [ ] New feature (adds non-breaking functionality)
• [ ] Breaking change (alters existing functionality)
• [ ] UI/UX improvement (enhances user interface without altering functionality)
• [ ] Refactor (improves code quality without altering functionality)
• [x] Documentation update
• [ ] Other (please describe below)

---

Checklist

• [ ] I have verified the accessibility of my changes
• [ ] I have tested all possible scenarios for this change
• [ ] I have updated theme.toml with a sane default for the feature
• [ ] I have made corresponding changes to the documentation:
  • [ ] Updated config.toml comments
  • [ ] Updated theme.toml comments
  • [ ] Updated "Mastering tabi" post in English
  • [ ] (Optional) Updated "Mastering tabi" post in Spanish
  • [ ] (Optional) Updated "Mastering tabi" post in Catalan

[welpo]

Thanks!