Clarify documentation on master-slave setup

[mbi]

With persistence in use, if the container is stopped and started, for the container continue to function as a slave you need to ensure that REPLICATION_MODE=slave is defined in the containers environment. In the absense of which the slave configuration will be turned off and the node will allow writing to it while having the last synced data from the master.

Is this the recommended way of promoting a slave to a master, in case of failure of the master node?
I.e.:

• Run both the master and the slave with persistence
• In case of failure of the master, restart the slave without REPLICATION_MODE
• Add a new slave to point the newly promoted master

Thank you.