MAINTAINERS: add entries for some documentation scripts

There are some documentation scripts I wrote with doesn't
have any maintainer at maintainer's file.

Add them to the DOCUMENTATION entry, in order to have
Jon and linux-doc ML c/c on those patches, plus a new
entry to ensure that I'll be c/c when people send patches
to those.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>