Added type parameter description to the readme file

Author: rcmadhankumar

README.md

@@ -22,6 +22,7 @@ There are several optional parameters that could be passed into ``` CreateVolume
 
 | **Parameters** | **Values** | **Default** | **Description**|
 | ----------------------------- | ----------------------------- | ----------- | ----------------------------- |
+| "type" | tier1, tier3 | tier1 | PowerVS Disk type that will be created during volume creation |
 | "csi.storage.k8s.io/fstype" | xfs, ext2, ext3, ext4 | ext4 | File system type that will be formatted during volume creation. This parameter is case sensitive! |