WIP Add customerize doc

[ianphil]

All Submissions:

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• [YES/NO] Have you followed the guidelines in our Contributing document?
• [YES/NO] Have you added an explanation of what your changes do and why you'd like us to include them?
• [YES/NO] I have updated the documentation accordingly.
• [YES/NO/NA] I have added tests to cover my changes.
• [YES/NO/NA] All new and existing tests passed.
• [YES/NO/NA] My code follows the code style of this project.
• [YES/NO/NA] I ran lint checks locally prior to submission.
• [YES/NO] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

What is the current behavior?

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Issue Number: N/A

What is the new behavior?

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Does this introduce a breaking change?

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• [YES/NO]

Any relevant logs, error output, etc?

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Other information

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