clk.txt: standardize document format

clk.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:

- Use section/title markups;
- Use :Author: for authorship;
- Mark literals and literal blocks;
- Mark tables;
- Use ReST notation for footnotes.

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