docs: improvements to the home page

[lostmygithubaccount]

The Ibis project home page is better than it once was [citation needed], but
can use some improvements. In particular, it'd be great if we could have an
interactive demo similar to
DuckDB's.
This would required PyArrow in
Pyodide as the last blocker, I
think.

Regardless, we should ensure the landing page answers to a new/prospective user:

• What is Ibis?
• Why should I use Ibis?
• Confidence Ibis is a well-supported, production-ready library

Unfortunately, this may involve more HTML/CSS than I'm conformtable doing but
we'll figure something out.