Update example in Service.go
I've found that when using `Title` as per the example the following error is generated when I try to compile the DSL:
[design/design.go:55] invalid use of Title in service
Changing to `Description` solves the issue for me (running v3)
Description
@@ -26,7 +26,7 @@ import (
// Example:
//
// var _ = Service("divider", func() {
-// Title("divider service") // optional
+// Description("divider service") // optional
//
// Error("Unauthorized") // error that apply to all the service methods
// HTTP(func() { // HTTP mapping for error responses
