[DOC] Install fluid on GKE clusters

[zhujian7]

Provide a link to that doc page:

What is the defect and your suggestions on improvement:

When I tried to install fluid on a GKE cluster, I ran into several issues:

1. The default hostpath of kubelet kubeconfig path(/etc/kubernetes/kubelet.conf) is not right, for GKE the kubeconfig is in /var/lib/kubelet/kubeconfig
2. Error in csi-nodeplugin-fluid: unable to read certificate-authority /etc/srv/kubernetes/pki/ca-certificates.crt for default-cluster due to open /etc/srv/kubernetes/pki/ca-certificates.crt: no such file or directory, it is required to mount the /home/kubernetes/bin/gke-exec-auth-plugin and /etc/srv/kubernetes/pki/ca-certificates.crt into the csi-nodeplugin-fluid
3. Error in daemonset demo-fuse: Error creating: insufficient quota to match these scopes: [{PriorityClass In [system-node-critical system-cluster-critical]}], the helm value runtime.criticalFusePod should be set to false.

[fengshunli]

criticalFusePod can be manually set during helm installation --set runtime.criticalFusePod=false