Add link to Kubeflow Notebook Server configuration recipe

[ptitzler]

This PR adds a link to the Kubeflow Notebook Server configuration recipe to the installation guide to make it more easily discoverable. the assumption is that a user might look in the installation guide for this type of content instead of the recipes, which are not organized by domain.

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[elyra-bot]

Thanks for making a pull request to Elyra!

To try out this branch on binder, follow this link:

[kevin-bates]

LGTM