docs(concerto): clarify relationship serialization phrasing in model-relationships (closes #350)

[Swastik092]

Closes #

Changes

Flags

Screenshots or Video

Related Issues

• Issue #
• Pull Request #

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to master from fork:branchname
• Manual accessibility test performed
  • Keyboard-only access, including forms
  • Contrast at least WCAG Level A
  • Appropriate labels, alt text, and instructions