landlock: Clarify documentation for the LANDLOCK_ACCESS_FS_REFER right

Clarify the "refer" documentation by splitting up a big paragraph of
text.

- Call out specifically that the denial by default applies to ABI v1 as
  well.
- Turn the three additional constraints for link/rename operations
  into bullet points, to give it more structure.

Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20230221165205.4231-1-gnoack3000@gmail.com


Signed-off-by: Mickaël Salaün <mic@digikod.net>