Is your feature request related to a problem or challenge?

The page in the docs https://datafusion.apache.org/library-user-guide/extending-operators.html says "Coming soon", however we have added to the 45 blog examples such as the uwheel and the Denormalized example which explains it.

Maybe we can just summarize one of these two posts to update the documentation, quoting the original source, after we have obtained authorization from the original authors?

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