EDAC, mce_amd_inj: Add README file

Provide information about each injection file and its usage for ease of
use and in-band documentation. This is a good idea adapted from ftrace.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: mchehab@osg.samsung.com
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: x86-ml <x86@kernel.org>
Link: http://lkml.kernel.org/r/1433277362-10911-7-git-send-email-Aravind.Gopalakrishnan@amd.com


Signed-off-by: Borislav Petkov <bp@suse.de>