ldm.txt: standardize document format

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

- Reformat its title;
- Use :Author: and :Last Updated: for authorship
- Use note markup;
- Reformat table to match ReST standard;
- Use bulleted lists where needed.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>