userguide: PV docs clarify Azure storage account restriction

Author: colemickens

docs/user-guide/persistent-volumes/index.md

@@ -532,7 +532,7 @@ parameters:
 
 * `skuName`: Azure storage account Sku tier. Default is empty.
 * `location`: Azure storage account location. Default is empty.
-* `storageAccount`: Azure storage account name. If storage account is not provided, all storage accounts associated with the resource group are searched to find one that matches `skuName` and `location`. If storage account is provided, `skuName` and `location` are ignored.
+* `storageAccount`: Azure storage account name. If storage account is not provided, all storage accounts associated with the resource group are searched to find one that matches `skuName` and `location`. If storage account is provided, it must reside in the same resource group as the cluster, and `skuName` and `location` are ignored.
 
 
 ## Writing Portable Configuration