Input: atarikbd - convert documentation into ReST format

This file require minimum adjustments to be a valid ReST file.
Do it, in order to be able to parse it with Sphinx.

We opted to remove section numbers, as this can be automatically
generated on Sphinx, by using :numbered: tag at index.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>