Documentation: ARCnet: Update obsolete contact info

Documentation: ARCnet: Update obsolete contact info

ARCnet docs states that inquiries on the subsystem should be emailed to
Avery Pennarun <apenwarr@worldvisions.ca>, for whom has been in CREDITS
since the beginning of kernel git history and her email address is
unreachable (bounce). The subsystem is now maintained by Michael
Grzeschik since c38f6ac74c9980 ("MAINTAINERS: add arcnet and take
maintainership").

In addition, there used to be a dedicated ARCnet mailing list but its
archive at epistolary.org has been shut down. ARCnet discussion nowadays
take place in netdev list. The arcnet.com domain mentioned has become
AIoT (Artificial Intelligence of Things) related Typeform page and
ARCnet info now resides on arcnet.cc (ARCnet Resource Center) instead.

Update contact information.

Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Link: https://patch.msgid.link/20251028014451.10521-2-bagasdotme@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>