Merge pull request #293 from RideReport/versions

Add versions endpoint.

Author: hunterowens

provider/README.md

@@ -41,6 +41,22 @@ Content-Type: application/vnd.mds.provider+json;version=0.3
 
 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.
 
+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:
+
+```http
+OPTIONS /trips/ HTTP/1.1 
+Host: provider.example.com 
+Accept: application/vnd.mds.provider+json;version=0.2,application/vnd.mds.provider+json;version=0.3;q=0.9
+```
+
+The response will include the most preferred supported version in the `Content-Type` header. For example, if only `0.3` is supported:
+
+```http
+Content-Type: application/vnd.mds.provider+json;version=0.3
+```
+
+The client can use the returned value verbatim as a version request in the `Accept` header.
+
 ### Response Format
 
 The response to a client request must include a valid HTTP status code defined in the [IANA HTTP Status Code Registry](https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml). It also must set the `Content-Type` header, as specified in the [Versioning](#Versioning) section.