Update readme to reflect ties to FAST project

[janechu]

Pull Request

📖 Description

This change cleans up the root level CONTRIBUTING.md file to point to FAST projects guidance as the two projects share a governing body.

✅ Checklist

General

• [ ] I have added tests for my changes.
• [ ] I have tested my changes.
• [x] I have updated the project documentation to reflect my changes.