Text update as per Azure#4657 (comment)

Author: darrinhodges

mahara-autoscale-cache/azuredeploy.json

@@ -228,7 +228,7 @@
                 "nfs"
             ],
             "metadata": {
-                "description": "File server type: GlusterFS, NFS--not yet highly available"
+                "description": "File server type: GlusterFS, NFS--not yet highly available. Gluster uses premium managed disks therefore premium skus are required."
             },
             "type": "string"
         },