docs: explain the value of deltalake on first page of docs

[braaannigan]

Description

The PR sets a proposed change to the text on the first page of the docs. When I arrived on these pages as a new user I found the current text did not answer the basic questions I had about the library. I've proposed a new text, though I'm happy to take on feedback.

Note: there is some overlap with the ideas on the "Why use delta lake" page. In essence I'm proposing having a quick summary of those concepts and a quickstart guide on the first page as I feel that for potential new users who have no familiarity with delta spark the current front page goes into more technical detail on that relationship than necessary.

I'd like to do a follow-on where the Why use delta lake page. I'm also wondering whether quickstart should be on a separate page in this section to make it easy to find.

Related Issue(s)

• closes #2996

[github-actions[bot]]

ACTION NEEDED

delta-rs follows the Conventional Commits specification for release automation.

The PR title and description are used as the merge commit message. Please update your PR title and description to match the specification.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 72.48%. Comparing base (25ce389) to head (6946514). Report is 6 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3017 +/- ## ========================================== + Coverage 72.47% 72.48% +0.01% ========================================== Files 128 128 Lines 40831 40831 Branches 40831 40831 ========================================== + Hits 29591 29598 +7 - Misses 9355 9357 +2 + Partials 1885 1876 -9 ```

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