[WIP] docs: restructure the docs index page

[MrPowers]

What changes were proposed in this pull request?

The Spark docs index page hasn't been updated in a while and this PR cleans up the language and shifts the examples from RDDs => DataFrames.

If this PR gets merged, I would like to take another stab and give even more detailed installation instructions. Showing users how to run scripts from the command line is cool, but I think it would also be nice to explain how to include Spark in a Python project and run a Jupyter notebook with Spark.

Why are the changes needed?

We'd like to encourage users to use DataFrames instead of RDDs.

This post ranks for "spark install" searches and we would also like to make it easier for users to install Spark.

Does this PR introduce any user-facing change?

No user facing code changes, but this would be user facing docs changes.

How was this patch tested?

Ran the code locally.

Was this patch authored or co-authored using generative AI tooling?

No

[srowen]

Looks good - ideally post a little before and after screenshot (or, just after)

[github-actions[bot]]

We're closing this PR because it hasn't been updated in a while. This isn't a judgement on the merit of the PR in any way. It's just a way of keeping the PR queue manageable. If you'd like to revive this PR, please reopen it and ask a committer to remove the Stale tag!