Fix man zpool property feature_guid

Fix man zpool property feature_guid

The property name gets mangled with the explanation due to the property
length.  Fixed by putting the explanation on the next line.

Before:
  unsupported@feature_Info rmation about unsupported features that are
  enabled on the pool. See zpool-features(5) for details.

After:
  unsupported@feature_guid
  Information about unsupported features that are enabled on the pool. See
  zpool-features(5) for details.

Signed-off-by: SenH <sen@senhaerens.be>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2419