doc: add very basic libcdio documentation

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit dc315cdb4ecffb7ec4d3496f1d0c8d0c123f0a7b)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Changelog: highlighting for 2.3.1

Suggested-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>