Add eu parameter to the API docs

[simonauner]

This is a simple documentation fix that adds the eu parameter to API.md as it was missing.

Checklist

• run npm run test
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows Code Of Conduct

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.