security: fix LSM description location

Acked-by: Kees Cook <keescook@chromium.org>

Fix Documentation location reference for where LSM descriptions should
be placed.

Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: James Morris <james.morris@microsoft.com>