docs: kernel-doc.rst: better describe kernel-doc arguments

Add a new section to describe kernel-doc arguments,
adding examples about how identation should happen, as failing
to do that causes Sphinx to do the wrong thing.

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