Review landing page for Kernel documentation

[AnneCYH]

Hi @stephensp ,

This site is meant to replace the current kteam-docs build:
https://canonical-kteam-docs.readthedocs-hosted.com/en/public/index.html

I started from an empty repository due to the many changes that have happened in the Canonical documentation starter pack so it's a WIP.

But I would like you to review the landing page content please:
https://canonical-kernel-docs.readthedocs-hosted.com/en/latest/

Instead of "kernel team" i think it can be about just the "kernel" but the overview does indicate who the documentation would be useful for.

Any feedback would be helpful, thanks!