docs: userspace-api: landlock.rst: avoid using ReST :doc:foo markup

The :doc:`foo` tag is auto-generated via automarkup.py.
So, use the filename at the sources, instead of :doc:`foo`.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/24888a9c5da3c505b2bc274fcd83be348dbaf972.1623824363.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Author: mchehab

Documentation/userspace-api/landlock.rst

@@ -145,7 +145,8 @@ Bind mounts and OverlayFS
 
 Landlock enables to restrict access to file hierarchies, which means that these
 access rights can be propagated with bind mounts (cf.
-:doc:`/filesystems/sharedsubtree`) but not with :doc:`/filesystems/overlayfs`.
+Documentation/filesystems/sharedsubtree.rst) but not with
+Documentation/filesystems/overlayfs.rst.
 
 A bind mount mirrors a source file hierarchy to a destination.  The destination
 hierarchy is then composed of the exact same files, on which Landlock rules can
@@ -170,8 +171,8 @@ Inheritance
 
 Every new thread resulting from a :manpage:`clone(2)` inherits Landlock domain
 restrictions from its parent.  This is similar to the seccomp inheritance (cf.
-:doc:`/userspace-api/seccomp_filter`) or any other LSM dealing with task's
-:manpage:`credentials(7)`.  For instance, one process's thread may apply
+Documentation/userspace-api/seccomp_filter.rst) or any other LSM dealing with
+task's :manpage:`credentials(7)`.  For instance, one process's thread may apply
 Landlock rules to itself, but they will not be automatically applied to other
 sibling threads (unlike POSIX thread credential changes, cf.
 :manpage:`nptl(7)`).
@@ -278,7 +279,7 @@ Memory usage
 ------------
 
 Kernel memory allocated to create rulesets is accounted and can be restricted
-by the :doc:`/admin-guide/cgroup-v1/memory`.
+by the Documentation/admin-guide/cgroup-v1/memory.rst.
 
 Questions and answers
 =====================
@@ -303,7 +304,7 @@ issues, especially when untrusted processes can manipulate them (cf.
 Additional documentation
 ========================
 
-* :doc:`/security/landlock`
+* Documentation/security/landlock.rst
 * https://landlock.io
 
 .. Links