Swap Rebalance behaviour clarification

In the docs on Swap Rebalance (https://docs.couchbase.com/server/current/learn/clusters-and-availability/rebalance.html, and https://docs.couchbase.com/server/current/install/upgrade-online.html#swap-rebalance-example) it would be worth mentioning that Active data is moved between the nodes being swapped, but replicas still need to be rebuilt (this means that there is some data transfer between nodes not being swapped).

This is important to highlight, since in the UI when rebalance progress is shown, you can see items leaving the nodes not involved in the swap rebalance.