Info for moderators

@explorerleslie , @cahrens , @gwprice , @srpearce , please take a look! HTML version here: http://draft-cohorts.readthedocs.org/en/latest/cohorts/cohorts_discussions.html
This implies that you need to both add a new cohort group AND move all students from the old group to the new group. Is that right or am I missing something her?