We tell the user how to rebuild the registries and how to start them.  But by itself all this does is give the user the same registry they would otherwise have.  We could combine these instructions with another set, say 'Building a custom plugin and adding it to the custom registry').  That would tell the user how to get some changed functionality from their custom registry.
So if time allows, I'd suggest something like this: * Explain the use case, how the user can put a custom plugin to use

• Explain how to build a custom plugin (we could use a trivial/simple example, something like a container that just offers a 'word count' script to count the number of words in the source directory, for example.  I think this could be accomplished by explaining how to start with a UBI image and adding to it a pretty easy bash script)
• Then show how to add the plugin to the custom registry
• Then reference the 'building the custom registry' existing instructions
• Lastly, show how to make use of the custom plugin (make a devfile that uses it) and show the results

 https://www.eclipse.org/che/docs/che-7/administration-guide/customizing-the-registries/