documentation: Update #nouveau IRC channel network

Like many free software projects, Nouveau recently moved from Freenode
to OFTC. Update the reference.

v3: Add acks.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210725150007.2818-1-alyssa@rosenzweig.io