Docs: Changes to main index page (Diátaxis) (#10186)
* Remove old user docs index page "wall of links"
* Remove item referencing to removed index page headline, less is more
* Adds an orphaned tutorial section index, bootstrap the first Diataxis-based main page content
* Update link
* WIP: More content for index page
* A suggestion of links for all main page entries
* Populate the tutorial index with some rough texts
* Add toctree to guide index
* Only index
* Wrap up initial landing page changes
* Polish sentences, remove old mentioning of features in the intro
* Lots of little cleanup
* Lots more word cleanup
* Apply suggestions from @agjohnson code review
Co-authored-by: Anthony <aj@ohess.org>
* Swap PR and cross-reference how-to
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Co-authored-by: Eric Holscher <eric@ericholscher.com>
Co-authored-by: Anthony <aj@ohess.org>
