Merge pull request #1 from sidfeiner/migration-route-type

Update migration-from-spray.md

docs/src/main/paradox/scala/http/migration-guide/migration-from-spray.md

@@ -68,6 +68,18 @@ All APIs are also available for Java. See everything under the `akka.http.javads
 
 ## Other changes
 
+
+### Changes in Route type
+
+Route type has changed from `Route = RequestContext ⇒ Unit` to `Route = RequestContext ⇒ Future[RouteResult]`.
+Which means that now we must complete the Request inside the controller and we can't simply pass the request to another Actor and complete it there.
+This has been done intentionally because in Spray people would forget to complete requests but the code would still compile.
+
+The following article mentions a few ways for us to complete the request based on processing outside the controller: 
+https://markatta.com/codemonkey/blog/2016/08/03/actor-per-request-with-akka-http/
+
+This article was written by Johan Andrén, a member of the akka-http team.
+
 ### Changes in Marshalling
 
 Marshaller.of can be replaced with `Marshaller.withFixedContentType`.