The notes there are somewhat confusing and assumes that the
reader would have read the DVBv3 way. This is not true anymore,
as the DVBv3 is now on a separate section that is marked as
deprecated.

So, cleanup the notes.

While here, add a note about using libdvbv5, instead of using
the DVBv5 API directly.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>