merged go-subscriptions-bstat into go-recurly

also added a README file

should be merged at the same time as:
* https://github.com/GigaOM/gigaom/pull/5354
* https://github.com/GigaOM/gigaom-plugins/pull/2684
* https://github.com/GigaOM/go-subscriptions/pull/20
* https://github.com/GigaOM/go-local-subscriptions/pull/1

as part of https://github.com/GigaOM/legacy-pro/issues/4055