A while ago I created, and have been maintaining, the section on HTTP at
https://docs.webplatform.org/wiki/http with similar goals.
I've also just finished RESTful Web APIs by Leonard Richardson and Mike Amundsen, this has everything I could want to put into an API book and then some. It's fantastic. I just wish there was a collection of this information on the Web somewhere (and indeed, this is what I hope to turn Web Platform Docs into). (I would still call it a service, though: I consider the Web a single application containing multiple services, or servers. History should have gone with "SOAP API" and "Hypermedia Service", not the other way around!)
On Web Platform Docs, I'd like to fill out more details on HTTP before going more abstract into hypermedia. The wiki already has extensive documentation on the de-facto hypermedia format (HTML) so hypermedia will obviously become a topic. Other hypermedia formats like JSON-LD have become W3C Recommendations too, so I don't think there'd be any problem with detailing hypermedia services/APIs in the long run.
If anyone has any contributions, by all means, be bold!
Austin Wright.