Add links to volumes from persistent volumes

When working with persistent volumes, I have to refer to the persitent
volumes page now and then, only to find that the information I need is
on a different page. The PR

- adds some links to ease navigation and
- currects the spelling of volume types, for example, `iscsi` is the type
  to specify rather than `iSCSI`,
- sort the volume type list in alphabetic order.
- added `photonPersistentDisk` as one of valid persistent volume type to
  use, though we don't have any documentation other than API spec for it.

content/en/docs/concepts/storage/persistent-volumes.md

@@ -308,28 +308,37 @@ If expanding underlying storage fails, the cluster administrator can manually re
 
 ## Types of Persistent Volumes
 
-PersistentVolume types are implemented as plugins.  Kubernetes currently supports the following plugins:
+PersistentVolume types are implemented as plugins. Kubernetes currently supports the following plugins:
 
-* GCEPersistentDisk
+* [`awsElasticBlockStore`](/docs/concepts/storage/volumes/#awselasticblockstore) - AWS Elastic Block Store (EBS)
-* AWSElasticBlockStore
+* [`azureDisk`](/docs/concepts/sotrage/volumes/#azuredisk) - Azure Disk
-* AzureFile
+* [`azureFile`](/docs/concepts/storage/volumes/#azurefile) - Azure File
-* AzureDisk
+* [`cephfs`](/docs/concepts/storage/volumes/#cephfs) - CephFS volume
-* CSI
+* [`cinder`](/docs/concepts/storage/volumes/#cinder) - Cinder (OpenStack block storage)
-* FC (Fibre Channel)
+  (**deprecated**)
-* FlexVolume
+* [`csi`](/docs/concepts/storage/volumes/#csi) - Container Storage Interface (CSI)
-* Flocker
+* [`fc`](/docs/concepts/storage/volumes/#fc) - Fibre Channel (FC) storage
-* NFS
+* [`flexVolume`](/docs/concepts/storage/volumes/#flexVolume) - FlexVolume
-* iSCSI
+* [`flocker`](/docs/concepts/storage/volumes/#flocker) - Flocker storage
-* RBD (Ceph Block Device)
+* [`gcePersistentDisk`](/docs/concepts/storage/volumes/#gcepersistentdisk) - GCE Persistent Disk
-* CephFS
+* [`glusterfs`](/docs/concepts/storage/volumes/#glusterfs) - Glusterfs volume
-* Cinder (OpenStack block storage)
+* [`hostPath`](/docs/concepts/storage/volumes/#hostpath) - HostPath volume
-* Glusterfs
+  (for single node testing only; WILL NOT WORK in a multi-node cluster;
-* VsphereVolume
+  consider using `local` volume instead)
-* Quobyte Volumes
+* [`iscsi`](/docs/concepts/storage/volumes/#iscsi) - iSCSI (SCSI over IP) storage
-* HostPath (Single node testing only -- local storage is not supported in any way and WILL NOT WORK in a multi-node cluster)
+* [`local`](/docs/concepts/storage/volumes/#local) - local storage devices
-* Portworx Volumes
+  mounted on nodes.
-* ScaleIO Volumes
+* [`nfs`](/docs/concepts/storage/volumes/#nfs) - Network File System (NFS) storage
-* StorageOS
+* `photonPersistentDisk` - Photon controller persistent disk.
+  (This volume type no longer works since the removal of the corresponding
+  cloud provider.)
+* [`portworxVolume`](/docs/concepts/storage/volumes/#portworxvolume) - Portworx volume
+* [`quobyte`](/docs/concepts/storage/volumes/#quobyte) - Quobyte volume
+* [`rbd`](/docs/concepts/storage/volumes/#rbd) - Rados Block Device (RBD) volume
+* [`scaleIO`](/docs/concepts/storage/volumes/#scaleio) - ScaleIO volume
+  (**deprecated**)
+* [`storageos`](/docs/concepts/storage/volumes/#storageos) - StorageOS volume
+* [`vsphereVolume`](/docs/concepts/storage/volumes/#vspherevolume) - vSphere VMDK volume
 
 ## Persistent Volumes