Clarify how to include snapshots in the `zpool list` output by
referencing the full name of the `listsnapshots` pool property,
and the `zpool list -t snapshot` option.
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#11562Closes#11565
d66f017c17