chore: update readme (NUL-1468)

[andsnw]

Description

Small updates for README on custom header usage with examples.

Linked Issues & PRs

• resolves
• relates to

GitHub Issue Linking Docs

Checklist

• [ ] I have added one of the patch, minor, major or no-release labels
• [ ] I have linked an issue from this repository using the Development option
• [ ] I have performed a self-review of my own code
• [ ] I have checked for redundant or commented out code
• [ ] I have commented my code where I can't make it self-documenting
• [ ] I have made corresponding changes to the documentation
• [ ] I have added any appropriate tests