Install: Improve page about container use (Docker, Podman)

### Documentation feedback

- Page title: Container Setup
- Page URL: https://cratedb.com/docs/guide/install/container/index.html
- Source: https://github.com/crate/cratedb-guide/blob/main/docs/install/container/index.rst

---

While [this page](https://cratedb.com/docs/guide/install/container/) primarily demonstrates how to invoke a single-node CrateDB instance, [that page](https://cratedb.com/docs/guide/install/container/docker.html) primarily demonstrates how to invoke a cluster made of multiple nodes.

On the latter page, [best practices](https://cratedb.com/docs/guide/install/container/docker.html#best-practices), [troubleshooting](https://cratedb.com/docs/guide/install/container/docker.html#id2), and [resource constraints](https://cratedb.com/docs/guide/install/container/docker.html#resource-constraints) come a bit too late / are too far away. Let's bring this crucial information from the full guide to the index page on a section called "general information", instead.

Along the lines, a share of copy-editing is certainly applicable, also after converting from reStructuredText to Markdown. Those resources haven't been touched for a while already: Now that the documentation system gained an update primarily about responsive design including design elements, there are various ways to improve guidance.

- Possibly related: GH-390

/cc @matriv, @grbade