MB-9728: Add reblance option help text

Change-Id: I1df3148bf2a0d83c17f64fff53d5e704eae94766
Reviewed-on: http://review.couchbase.org/31309
Reviewed-by: Steve Yen <steve.yen@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>