docs-rst: convert lsm from DocBook to ReST

This file is outdated. Still, as it is the only one left at
DocBook dir, convert it, and store it, with a .txt extension,
under Documentation/lsm.txt.

This way, we can get rid of DocBook from the building system,
without needing to wait for someone to take care of it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/00-INDEX

@@ -264,6 +264,8 @@ logo.gif
 	- full colour GIF image of Linux logo (penguin - Tux).
 logo.txt
 	- info on creator of above logo & site to get additional images from.
+lsm.txt
+	- Linux Security Modules: General Security Hooks for Linux
 lzo.txt
 	- kernel LZO decompressor input formats
 m68k/