Correct cni path in k3s.rst for rancher desktop

[RichardoC]

Correct cni path in k3s installation documentation for rancher desktop

[RichardoC]

This was discovered by following https://docs.cilium.io/en/stable/gettingstarted/k8s-install-default/#k8s-install-quick on an M1 macbook, with Rancher Desktop 1.9.1

Failure message when try to create pods post installation if you don't add this flag is below

$ kubectl get pods
NAME                                     READY   STATUS              RESTARTS        AGE
somepod-77ccd57875-6pr7s                 0/1     ContainerCreating   0               30s
$ kubectl describe pods
.....
Events:
  Type     Reason                  Age                    From               Message
  ----     ------                  ----                   ----               -------
  Warning  FailedCreatePodSandBox  8m9s                   kubelet            Failed to create pod sandbox: rpc error: code = Unknown desc = failed to setup network for sandbox "77b80d18d8cee329081f8917125494de0a711c241bc38817835b854b8a6014f3": plugin type="cilium-cni" failed (add): failed to find plugin "cilium-cni" in path [/usr/libexec/cni]
  Normal   SandboxChanged          2m58s (x25 over 8m9s)  kubelet            Pod sandbox changed, it will be killed and re-created.

[lambdanis]

/test