Update docs to reflect optional parameter --subscription to retrieve the Fully Qualified Domain Name of the CycleServer VM.

[tomaslaz]

I have to explicitly provide the name of the subscription that the resource group belongs to. I am not sure why this is the case for me but I assume this will be the case for similar accounts for other universities/institutes when people are assigned to multiple subscriptions.

[tomaslaz]

https://docs.microsoft.com/en-us/azure/cyclecloud/quickstart-install-cyclecloud

Section: Log into the CycleCloud Application Server

It says "To retrieve the Fully Qualified Domain Name (FQDN) of the CycleServer VM from either the Azure Portal or using the CLI":

export RESOURCE_GROUP="MyQuickstart"
az network public-ip show -g ${RESOURCE_GROUP?} -n cycle-ip --query dnsSettings.fqdn

I had to provide the name of the subscription that the resource group belongs to as follows:

export RESOURCE_GROUP="MyQuickstart"
export SUBSCRIPTION_NAME="My Subscription"

az network public-ip show --subscription "$SUBSCRIPTION_NAME" -g ${RESOURCE_GROUP?} -n cycle-ip --query dnsSettings.fqdn