Add help message indicating {create,delete}-firewall is not necessary

[ahmetb]

First time I ran kubehost -h these commands confused me:

  create-firewall <service>  : Create a GCP firewall rule for the hostPort
                               deployment created with 'bind'.
  delete-firewall <service>  : Delete a GCP firewall rule for the hostPort
                               deployment created with 'bind'.

I think they are "not needed" if you're using bind/unbind.

Please consider adding a note to these cmds saying something in the lines of:

Not needed if you use bind/unbind.

[WilliamDenniss]

Good point.