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.
Qiming Teng
9ddc0a3ad9