add prerequisit  to have permissions to create service principals in the subscription
acs-engine hangs with "WARN[0008] apimodel: ServicePrincipalProfile was empty, assigning role to application..."
if user does not have enough permissions to create and assign service principals ans azure applications
@@ -19,6 +19,7 @@ After the cluster is deployed the upgrade and [scale](scale.md) commands can be
## Gather Information
* The subscription in which you would like to provision the cluster. This is a uuid which can be found with `az account list -o table`.
+* Proper access rights within the subscription. Especially the right to create and assign service principals to applications ( see ACS Engine the Long Way, Step #2)
* A `dnsPrefix` which forms part of the the hostname for your cluster (e.g. staging, prodwest, blueberry). The DNS prefix must be unique so pick a random name.
* A location to provision the cluster e.g. `westus2`.
