command-list.txt: add gitfaq to the list of guides

When 'gitfaq.txt' was added in 2149b6748f (docs: add a FAQ, 2020-03-30), it was added to the Makefile but not to command-list.txt. Add it there also, so that the new FAQ is listed in the output of `git help --guides`. Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>