Add some comments

server/handler.go

@@ -4,12 +4,23 @@ import (
 	"github.com/micro/go-micro/registry"
 )
 
+// Handler interface represents a Service request handler. It's generated
+// by passing any type of public concrete object with methods into server.NewHandler.
+// Most will pass in a struct.
+// Example:
+// type Service struct {}
+// func (s *Service) Method(context, request, response) error {
+//	return nil
+// }
+//
 type Handler interface {
 	Name() string
 	Handler() interface{}
 	Endpoints() []*registry.Endpoint
 }
 
+// Subscriber interface represents a subscription to a given topic using
+// a specific subscriber function or object with methods.
 type Subscriber interface {
 	Topic() string
 	Subscriber() interface{}

server/server.go

@@ -66,6 +66,15 @@ func NewSubscriber(topic string, h interface{}) Subscriber {
 }
 
 // Creates a new handler interface using the default server
+// Handlers are required to be a public object with public
+// methods. Call to a service method such as Foo.Bar expects
+// the type:
+//
+// type Foo struct {}
+// func (f *Foo) Bar(ctx, req, rsp) error {
+// 	return nil
+// }
+//
 func NewHandler(h interface{}) Handler {
 	return DefaultServer.NewHandler(h)
 }