Remove duplicate paragraphs and merge the relevant sections

[rylurk]

Describe this PR

The opening two paragraphs of the ‘Relation fields’ section are word for word copies of the opening two paragraphs in the ‘Terminology’ section.

I think the readability of this page would improve a lot if these two sections were merged together, for the reason stated above and because the ‘Terminology’ section is exclusively about relation fields anyway.

Changes

[vercel[bot]]

@rylurk is attempting to deploy a commit to the Prisma Team on Vercel.

A member of the Team first needs to authorize it.

[netlify[bot]]

✅ Deploy Preview for prisma2-docs ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	860da6da6aa2b9f9460cf5e04ddab7430bc1c1f3
🔍 Latest deploy log	https://app.netlify.com/sites/prisma2-docs/deploys/62f9476e443e780008db1ada
😎 Deploy Preview	https://deploy-preview-3598--prisma2-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[ObamaTheLlama114]

thank you for your contribution