Update the disable documentation in two places

[nep]

Overview

Clarified the implications of disabling custom fields and relationships in the documentation.

Nature of This Change

• [ ] 🐛 Fixes a bug
• [ ] 🚀 Implements a new feature
• [ x ] 🛁 Rewrites existing documentation
• [ ] 💅 Fixes coding style
• [ ] 🔥 Removes unused files / code