Confirm runc support / update installation docs

### TL;DR

Podman [installation documentation] indicates that both `crun` and `runc` are supported, but some PRs closed in 2024 ([PR#22706], [PR#23020]) indicate support for `runc` was dropped, and the release note was never propagated to any release.

---
### Details

Having recently submitted a PR to update some documentation in Podman which resulted in some Cirrus CI failures ([PR#25111]), I wanted to get a better understanding of the tests. I had been linked to the [`.cirrus.yml`] file and I was skimming it when my eyes were immediately drawn to [the following line]:

```yml
CI_DESIRED_RUNTIME: crun # As of 2024-05-28 there are no other supported runtimes
```

I was mildly horrified to see this, as I had just submitted (and had approved and merged!) my first podman.io PR a few days ago ([PR#363]), and one of the items on my PR was to switch FROM `crun` to `runc` when installing Podman from source on Debian, due to an error I ran into doing so (_`crun unknown version specified`_). I turned on Blame so I could figure out what was going on and found the following PRs removing runc support:

* https://github.com/containers/podman/pull/22706
* https://github.com/containers/podman/pull/23020

[PR#22706] has the following release note in the body:

> Podman no longer supports runc nor cgroups v1

However, I checked every Release after the date that was merged, and all of the tags linked to the commit, and I could not find any evidence of this release note making it "public".

---
### What to do?

In conclusion, this issue is to track whether or not Podman supports `runc`, and if not, track the need to update the [installation documentation] (I am willing to take this on, if not just to correct my "mistake"). I am guessing there will need to be a corresponding issue in Podman, as I see `runc` all over it (I am definitely not the best person for this task).

[installation documentation]: https://podman.io/docs/installation#crun--runc
[PR#22706]: https://github.com/containers/podman/pull/22706
[PR#23020]: https://github.com/containers/podman/pull/23020
[PR#25111]: https://github.com/containers/podman/pull/25111
[`.cirrus.yml`]: https://github.com/containers/podman/blob/main/.cirrus.yml
[the following line]: https://github.com/containers/podman/blob/6ee51c5e4fcc17b86388dba2bcd05b9f0f18b80d/.cirrus.yml#L61
[PR#363]: https://github.com/containers/podman.io/pull/363

Start with .cirrus.yml and the linked PRs #22706 and #23020 to verify the current runc and crun support status. Then compare that finding with the installation documentation at the linked crun--runc section; done means the documented support and any relevant release information match the confirmed project behavior.

Written by the indexing model from the issue text.