docs: 00-INDEX: consolidate process/ and admin-guide/ description

Instead of having descriptions for individual files inside
the process/ and admin-guide/ documentation, consolidate them
into one entry per directory, just like other descriptions
inside 00-INDEX.

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