Merge pull request #26 from duffelhq/docs-link

Link to our RubyDoc.info docs from the README

Author: Tim Rogers

README.md

@@ -1,5 +1,7 @@
 # Duffel API Ruby client library
 
+[![RubyDoc.info documentation](http://img.shields.io/badge/yard-docs-blue.svg)](https://rubydoc.info/github/duffelhq/duffel-api-ruby)
+
 A Ruby client library for the [Duffel API](https://duffel.com/docs/api).
 
 ## Contents
@@ -236,4 +238,8 @@ else
 end
 ```
 
+## Learn more
+
+You can find complete documentation on this library's classes and methods in the in-code
+documentation on [RubyDoc.info](https://rubydoc.info/github/duffelhq/duffel-api-ruby).