Document the APIs it interacts with

[donpdonp]

At first glance it looks like an order book with no hooks to financial services. In browsing the code there is a banks.yml and pecunix reference. It'd be helpful if the README talked about the features available to transfer into and out of bitcoin-central.

[davout]

Well, actually, the best approach would be to have pluggable modules that take care of interacting with third parties and dealing with all the method specifics