Documentation: fix security related doc refs

Make security document refs valid.

Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/security/credentials.rst b/Documentation/security/credentials.rst
index 038a7e19..66a2e24 100644
--- a/Documentation/security/credentials.rst
+++ b/Documentation/security/credentials.rst
@@ -196,7 +196,7 @@
      When a process accesses a key, if not already present, it will normally be
      cached on one of these keyrings for future accesses to find.
 
-     For more information on using keys, see Documentation/security/keys.txt.
+     For more information on using keys, see ``Documentation/security/keys/*``.
 
  5. LSM