Add a link for installing Cilium in RKE

[amitmavgupta]

Rancher Manager update

The Rancher Manager* documentation is moving. Please file any issues or pull requests at https://github.com/rancher/rancher-docs instead.

• = content/rancher

K3s update

The K3s* documentation is moving. Please file any issues or pull requests at https://github.com/k3s-io/docs instead.

• = content/k3s

[amitmavgupta]

@xmulligan