fix(Notion Node): Fix Relation ID description

[ayatnkw]

Summary

• Fix the wording of the description and add details about enabling two-way relations.

Related Linear tickets, Github issues, and Community forum posts

• https://community.n8n.io/t/i-cant-achieve-to-create-relation-ids-with-notion/63908/

Review / Merge checklist

• [ ] PR title and summary are descriptive. (conventions)
• [ ] Docs updated or follow-up ticket created.
• [ ] Tests included.
• [ ] PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)