Documentation: clarify the purpose of LSMs

Clarify the purpose of the LSM interface with some brief examples and
pointers to additional documentation.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/Documentation/security/credentials.txt b/Documentation/security/credentials.txt
index fc0366c..8625705 100644
--- a/Documentation/security/credentials.txt
+++ b/Documentation/security/credentials.txt
@@ -221,10 +221,10 @@
  (5) LSM
 
      The Linux Security Module allows extra controls to be placed over the
-     operations that a task may do.  Currently Linux supports two main
-     alternate LSM options: SELinux and Smack.
+     operations that a task may do.  Currently Linux supports several LSM
+     options.
 
-     Both work by labelling the objects in a system and then applying sets of
+     Some work by labelling the objects in a system and then applying sets of
      rules (policies) that say what operations a task with one label may do to
      an object with another label.