Add FAQs for debugging msgpack serialization issues

We often get questions about how to debug serialization issues. The first few times you face them it can be challenging to figure out what the problem is. With msgpack being a binary protocol, it's a bit more tricky to figure out than something like JSON would be. At this point though, we (core team) have a pretty well-established process for debugging these issues. We should write these steps up as an FAQ page to help people figure these problems out.