doc: release notes for 3.4.6 GA

Change-Id: I4981af8e82606ac0dea1560b3d0497d5a2a48ec1
BUG: 1125245
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/9015
Tested-by: Gluster Build System <jenkins@build.gluster.com>