Update guide on vm.swappiness values

Recent versions of the Linux kernel (3.5-rc1, RHEL/CentOS > 2.6.32-303) have [changed the behaviour vm.swappiness](http://www.mysqlperformanceblog.com/2014/04/28/oom-relation-vm-swappiness0-new-kernel/). A swappiness value of ```0``` in these kernel's will prevent swapping out 
anonymous memory, other than unpinned file backed pages, making it much more likely the the OOM killer will be activated rather than the desired behaviour of the kernel using swap space. A value of ```1``` will still allow the use of swap space in emergencies.