add cluster config example to docs

[jaffee]

Overview

We had some confusion over configuration - hopefully this will help to address it.

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• I have updated the documentation.
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• I have included tests that cover my changes.
• All new and existing tests pass.

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• Ensure that any changes to external docs have been included in this pull request.
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• Ensure the new code is properly commented and follows Idiomatic Go.
• Check that tests have been written and that they cover the new functionality.
• Run tests and ensure they pass.
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[yuce]

Looks good!