Error handling documentation

Please create some documentation specifying possible error/failures to operations, what they "look" like in the stats and what our recommendation is on how to handle them (pointing back to the relevant SDK documentation)

i.e. tmp_oom, "get miss" (it's technically a failure, let's make it overly obvious what it means), CAS failure, add() failure, replace() failure,

Some of this should be covered in the SDK material, but this bug is specifically for a single page where this information is aggregated that a customer/user could read about how to handle errors both on the server-side and the SDK side.