Added a note about replica order, minor phrasing.

Change-Id: I04c092ac88dd3baefdd4bf248b11809a6dd69363
Reviewed-on: http://review.couchbase.org/27350
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>