MB-8663 Add an entry to CHANGES file about XDCR settings.

Change-Id: I77ba4992a6febb7db23eb1cf172a8acefb5e6d37
Reviewed-on: http://review.couchbase.org/28552
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>