docs-rst: convert lsm from DocBook to ReST

2017-05-16T11:44:19Z

This file is outdated.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

kernel/Documentation/lsm.txt, branch linux-4.15.y

docs-rst: convert lsm from DocBook to ReST