Clarify deployment of Spring Boot apps to App Engine Standard

Closes gh-13090

spring-boot-project/spring-boot-docs/src/main/asciidoc/deployment.adoc

@@ -400,9 +400,11 @@ identifier for you and also sets up HTTP routes. Add a Java app to the project a
 it empty and then use the https://cloud.google.com/sdk/downloads[Google Cloud SDK] to
 push your Spring Boot app into that slot from the command line or CI build.
 
-App Engine needs you to create an `app.yaml` file to describe the resources your app
-requires. Normally, you put this file in `src/main/appengine`, and it should resemble the
-following file:
+App Engine Standard requires one to use WAR packaging. Follow https://github.com/GoogleCloudPlatform/getting-started-java/blob/master/appengine-standard-java8/springboot-appengine-standard/README.md[these steps] to deploy App Engine Standard application to Google Cloud.
+
+App Engine Flex on the other hand requires you to create an `app.yaml` file to describe 
+the resources your app requires. Normally, you put this file in `src/main/appengine`, 
+and it should resemble the following file:
 
 [source,yaml,indent=0]
 ----
@@ -446,10 +448,6 @@ build configuration, as shown in the following example:
 Then deploy with `mvn appengine:deploy` (if you need to authenticate first, the build
 fails).
 
-NOTE: Google App Engine Classic is tied to the Servlet 2.5 API, so you cannot deploy a
-Spring Application there without some modifications. See the
-<<howto.adoc#howto-servlet-2-5,Servlet 2.5 section>> of this guide.
-
 
 
 [[deployment-install]]