Document running on Incus

[travier]

We should integrate this blog post into the docs: https://agnomi.net/posts/incus/fedora-coreos/

See also:

• https://discuss.linuxcontainers.org/t/fedora-coreos-guest-on-incus/25470
• https://discuss.linuxcontainers.org/t/how-to-run-fedora-coreos-as-an-lxd-vm/14399