Add a sentence explaining trocla password name formatting

First, add the Puppet class to the new server, and run puppet on that

server and on the storage server (currently `bungei`) to create the

replication password (stored in [trocla](howto/puppet/#password-management), on `pauli`):

replication password (stored in [trocla](howto/puppet/#password-management), on `pauli`).

The replication password is stored in the format

`<hostname>-main-5432-backup_role`. For example, the command to get the

replication password for the `postgresql-metrics-psqlts-01` host:

    trocla get postgresql-metrics-psqlts-01-main-5432-backup_role plain