Follow-up from "Handle Member Promotions When Block Seat Overages is Enabled"

The following discussion from !167358 (merged) should be addressed:

• @dstull started a discussion: (+1 comment)

  question:

  I watched the video and I see this message in the UI.

  Do you think we can add a bit more helpful context for the user here as to the why?

  Maybe something like this(may benefit from Technical Writing input):

            members.each { |m| m.errors.add(:base, 'Cannot update role to a higher level as it would take a seat and this top-level group is set to not allow <something about seat overages>') }