Add faq

So, I've started adding in a FAQ. It needs some help, but I think it's a good start. It might be a good idea to merge it in and just work on it collaboratively here, rather than in issues which don't actually keep track of versioning and don't lend themselves towards building a living document. 

Ideally, this would actually be part of the README which is the index of the website. What do you think?