The text has been expanded a bit to clarify that it is necessary to create identity files with an example before using the Docker image.
Changed the <identity-dir> placeholder to <multinode-identity-dir> so no one confuses them with the storagenode identity files.
Changed the <storage-dir> placeholder to <multinode-config-dir> so no one confuses them with the storagenode 'config' folder.
fixed#4547
