Add swappiness>0 recommendation to production notes

Hi,

“Swappiness” is a Linux kernel setting that influences the behavior of the Virtual Memory manager when it needs to allocate a swap, ranging from 0-100. A setting of “0“ tells the kernel to swap only to avoid out-of-memory problems. A setting of 100 tells it to swap aggressively to disk.

With kernel version 3.5 and over, as well as kernel version 2.6.32-303 and over, a value of "0" may cause swap not be used. It's best to recommend having a setting of "1".