Update the grafana instructions

[jbostian]

• There is a bind mount authority issue when starting the cAdvisor container:

$ docker run -v /:/rootfs:ro -v /var/run:/var/run:ro -v /sys:/sys:ro \
> -v /var/lib/docker/:/var/lib/docker:ro -v /dev/disk/:/dev/disk:ro \
> -p 8080:8080 -d --network monitoring --name=cadvisor cadvisor
docker: Error response from daemon: authorization denied by plugin zcxauthplugin: Request to bind mount the path "/" with ro mode is disabled for Docker running on IBM zCX appliance instance.
See 'docker run --help'.

• Same problem when starting nodeExporter:

$ docker run --name nodeexporter -v /proc:/host/proc:ro -v /sys:/host/sys:ro \
> -v /:/rootfs:ro -v /etc/hostname:/etc/host_hostname:ro -p 9100:9100 -d \
> --network monitoring nodeexporter
docker: Error response from daemon: authorization denied by plugin zcxauthplugin: Request to bind mount the path "/" with ro mode is disabled for Docker running on IBM zCX appliance instance.
See 'docker run --help'.

• Add a couple of simple usage notes:
  • On first login, specify userid/pwd of admin/admin. Then Grafana will let you set your real password.
  • Load the zCX dashboard from grafana.com:
    https://grafana.com/grafana/dashboards?search=zcx