docs: Update info about supported k8s version.
docs: Update info about supported k8s version.

Closes: #68

vefimova/virtlet,Mirantis/virtlet,Mirantis/virtlet,vefimova/virtlet,nhlfr/virtlet,nhlfr/virtlet,nhlfr/virtlet,vefimova/virtlet,vefimova/virtlet,nhlfr/virtlet