Documentation/SubmittingPatches: convert it to ReST markup

- Change the sections to use ReST markup;
- Add cross-references where needed;
- convert aspas to verbatim text;
- use code block tags;
- make Sphinx happy.

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