Added warning for cgroups to single node docker

[dgiebert]

Closes rancher/rancher-docs#46

[btat]

@snasovich could you please have someone from your team review this?

[lerminou]

the fix is not quite good, it should be better to explain this fix: I found the reason why rancher fails to start on cgroupv2

https://github.com/rancher/rancher/issues/36238#issuecomment-1232690242

BTW maybe move the documentation to prerequisites and not known issues