Update constants.md with examples

[swierczek]

Overview

Add examples of constant values and remove unused constant reference.

Nature of This Change

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