admin-guide/storage: finish second chapter.

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
Merge branch 'master' of github.com:eayun/Documents
admin-guide/storage: finish preparing NFS Storage

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
admin-guide/storage: finish add nfs storage

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>