text: Title: Attach documentation to API types and/or resources
  Body: Forked from #3060, based on [a comment](https://github.com/GoogleCloudPlatform/kubernetes/issues/3060#issuecomment-78361868) by @smarterclayton.
  
  Currently we can extract documentation from struct fields and represent them in the swagger for the API. We don't have a comparable mechanism for documenting whole types or resources. We'd like to be able to either directly embed documentation or at least link to API docs #3059.
  
  go-restful provides a way to attach documentation to operations, so we'd just need a Description() interface function on the registry to attach the info to operations on a resource.
  
  However, it would be nice to be able to put the documentation on the API types directly. The [swagger spec](https://github.com/swagger-api/swagger-spec/blob/master/versions/1.2.md) does have a way to represent descriptions of ["model objects"](https://github.com/emicklei/go-restful/blob/master/swagger/swagger.go#L170), but go-restful doesn't yet populate it.
  
  Go doesn't directly support tagging structs or types. We previously looked into some way to use godoc, but that looked very cumbersome.
  
  We need a way to document structs, custom types #2971, and enum-like constants.
  
  Perhaps we could develop a convention that would enable us to use the existing struct field tag mechanism, such as a tagged non-public/non-json "documentation" field (or anonymous field?), or a constant string whose name can be automatically derived from the type name.
  
  cc @nikhiljindal 
  