zpool-list.8: clarify that only imported pools are listed (#18352)

The man page stated "all pools in the system are listed" which is
misleading, as only imported pools are shown. Clarify this and
add a cross-reference to zpool-import(8) for discovering pools
available for import.

Signed-off-by: Christos Longros <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>

man/man8/zpool-list.8

@@ -48,7 +48,9 @@
 Lists the given pools along with a health status and space usage.
 If no
 .Ar pool Ns s
-are specified, all pools in the system are listed.
+are specified, all pools currently imported are listed.
+For listing pools available for import, see
+.Xr zpool-import 8 .
 When given an
 .Ar interval ,
 the information is printed every