Update driver-parameters.md

docs/driver-parameters.md

@@ -6,6 +6,7 @@
 Name | Meaning | Available Value | Mandatory | Default value
 --- | --- | --- | --- | ---
 source | Samba Server address | `//smb-server-address/sharename` </br>([Azure File](https://docs.microsoft.com/en-us/azure/storage/files/storage-files-introduction) format: `//accountname.file.core.windows.net/filesharename`) | Yes |
+createSubDir | create a sub dir for new volume | `true`, `false` | `false` |
 csi.storage.k8s.io/node-stage-secret-name | secret name that stores `username`, `password`(`domain` is optional) | existing secret name |  Yes  |
 csi.storage.k8s.io/node-stage-secret-namespace | namespace where the secret is | k8s namespace  |  Yes  |