doc: add documentation for the "Brick Failure Detection" feature

The documentation from the feature page should be included in the
sources.

Change-Id: I4fd67ce1c56afc5236c00de8be9110dfa6bbe91f
BUG: 1086700
Feature-page: http://www.gluster.org/community/documentation/index.php/Features/Brick_Failure_Detection
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/7449
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>