DOC: docs page should have more content

[d-v-b]

Describe the issue linked to the documentation

The landing page for the docs is a small introduction and a series of links:

There is actually no content here -- it's just links. But people come to the documentation for content.

Suggested fix for documentation

Instead of asking visitors to figure out which link they must click to get content, we should put some content on the main page (like a simple code example). Look at the pydantic docs landing page:

instead of foregrounding the links (which we do on the zarr docs), the links are pushed to the side, and the body of the page is content -- code examples and explanations. We should copy this.