WIP: Latency reduction checklist

It may be worth combining this section and the previous one, because the first mitigation for io and network problems is to check the aforementioned tunings (such as I/O scheduler and net.core settings in sysctl).  In this combined section, instances of blocked I/O or hitting swap or dropping packets would be the "things to watch for," with the tuning guides as first steps.  

If disk I/O in particular is pegged, this is a good section to mention "add more nodes" as a response to resource saturation, while simultaneously nodding to how easy that is to do in Riak.