doc: ReSTify and split LSM.txt

The existing LSM.txt file covered both usage and development, so split
this into two files, one under admin-guide and one under kernel
development.

Cc: James Morris <james.l.morris@oracle.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst
index 8c60a8a..e14c374 100644
--- a/Documentation/admin-guide/index.rst
+++ b/Documentation/admin-guide/index.rst
@@ -61,6 +61,7 @@
    java
    ras
    pm/index
+   LSM/index
 
 .. only::  subproject and html