Update 406 response when an invalid version is requested.

#313

provider/README.md

@@ -39,9 +39,9 @@ Content-Type: application/vnd.mds.provider+json;version=0.3
 
 > Since versioning was not added until the 0.3.0 release, if the `Content-Type` header is `application/json` or not set in the response, version `0.2` must be assumed.
 
-If an unsupported or invalid version is requested, the API must respond with a status of `406 Not Acceptable`. In which case, the response should include a body specifying a list of supported versions.
+If an unsupported or invalid version is requested, the API must respond with a status of `406 Not Acceptable`. If this occurs, a client can explicitly negotiate available versions.
 
-A client can explicitly negotiate headers using the `OPTIONS` method to an MDS endpoint. For example, to check if `trips` supports either version `0.2` or `0.3` with a preference for `0.2`, the client would issue the following request:
+A client negotiates available versions using the `OPTIONS` method to an MDS endpoint. For example, to check if `trips` supports either version `0.2` or `0.3` with a preference for `0.2`, the client would issue the following request:
 
 ```http
 OPTIONS /trips/ HTTP/1.1