Add doc for azure file

docs/concepts/storage/persistent-volumes.md

@@ -416,7 +416,7 @@ for provisioning PVs. This field must be specified.
 | Volume Plugin        | Internal Provisioner| Config Example                       |
 | :---                 |     :---:           |    :---:                             |
 | AWSElasticBlockStore | ✓            | [AWS](#aws)                          |
-| AzureFile            | ✓            | -                                    |
+| AzureFile            | ✓            | [Azure File](#azure-file)            |
 | AzureDisk            | ✓            | [Azure Disk](#azure-disk)            |
 | CephFS               | -                   | -                                    |
 | Cinder               | ✓            | [OpenStack Cinder](#openstack-cinder)|
@@ -706,6 +706,27 @@ parameters:
 * `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, it must reside in the same resource group as the cluster, and `skuName` and `location` are ignored.
 
+#### Azure File
+
+```yaml
+kind: StorageClass
+apiVersion: storage.k8s.io/v1
+metadata:
+  name: azurefile
+provisioner: kubernetes.io/azure-file
+parameters:
+  skuName: Standard_LRS
+  location: eastus
+  storageAccount: azure_storage_account_name
+```
+
+* `skuName`: Azure storage account Sku tier. Default is empty.
+* `location`: Azure storage account location. Default is empty.
+* `storageAccount`: Azure storage account name.  Default is empty.
+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.
+
+During provision, a secret will be created for mounting credentials. If the cluster has enabled both [RBAC](/docs/admin/authorization/rbac/) and [Controller Roles](/docs/admin/authorization/rbac/#controller-roles), you will first need to add `create` permission of resource `secret` for clusterrole `system:controller:persistent-volume-binder`.
+ 
 #### Portworx Volume
 
 ```yaml