kprobes.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:

- comment the contents;
- add proper markups for titles;
- mark literal blocks as such;
- use :Author: for authorship;
- use the right markups for footnotes;
- escape some literals that would otherwise cause problems;
- fix identation and add blank lines where needed.
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>