LU-3860 bug: fix kernel directory README.

The kernel patch README now points visitors to
http://lustre.opensfs.org/documentation/



Signed-off-by: Richard Henwood <richard.henwood@intel.com>
Change-Id: Ifbf3d71fc0c6f7ad99a09f19107ca99f5b445ce7
Reviewed-on: http://review.whamcloud.com/7499


Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>