admin-guide/storage: finish detaching export storage

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

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
admin-guide/storage: TODO for permissions of storage

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