linux-phytec-fsl

md: Update documentation for sync_min and sync_max entries

linux/Documentation/md.txt is missing description for sync_min and
sync_max entries.
This patch adds description for sync_min and sync_max entries.

Signed-off-by: Roman Ovchinnikov <coolthecold@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>