Better $ref documentation

Fixes #135

Author: webron

versions/2.0.md

@@ -1106,6 +1106,8 @@ description: Pets operations
 
 A simple object to allow referencing other definitions in the specification. It can be used to reference parameters and responses that are defined at the top level for reuse.
 
+The Reference Object is a [JSON Reference](http://tools.ietf.org/html/draft-pbryan-zyp-json-ref-02) that uses a [JSON Pointer](http://tools.ietf.org/html/rfc6901) as its value. For this specification, only [canonical dereferencing](http://json-schema.org/latest/json-schema-core.html#anchor27) is supported.
+
 ##### Fixed Fields
 Field Name | Type | Description
 ---|:---:|---