MAINTAINERS: mark linux-doc-tw-discuss mailing list moderated

MAINTAINERS: mark linux-doc-tw-discuss mailing list moderated

After sending a patch to linux-doc-tw-discuss@lists.sourceforge.net, I got
the typical response for a moderated list:

  Your mail to 'linux-doc-tw-discuss' with the subject
  ....
  Is being held until the list moderator can review it for approval.

  The reason it is being held:

      Post by non-member to a members-only list

Mark this mailing list moderated in MAINTAINERS.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20220713043516.19290-1-lukas.bulwahn@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>