Add callouts to Kotlin examples for parity

Author: sbrannen

framework-docs/src/docs/asciidoc/web/webflux-functional.adoc

@@ -640,14 +640,15 @@ RouterFunction<ServerResponse> route = route()
 [source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
 .Kotlin
 ----
-	val route = coRouter {
+	val route = coRouter { // <1>
 		"/person".nest {
 			GET("/{id}", accept(APPLICATION_JSON), handler::getPerson)
 			GET(accept(APPLICATION_JSON), handler::listPeople)
 			POST(handler::createPerson)
 		}
 	}
 ----
+<1> Create router using Coroutines router DSL; a Reactive alternative is also available via `router { }`.
 
 Though path-based nesting is the most common, you can nest on any kind of predicate by using
 the `nest` method on the builder.

framework-docs/src/docs/asciidoc/web/webmvc-functional.adoc

@@ -623,13 +623,14 @@ RouterFunction<ServerResponse> route = route()
 	import org.springframework.web.servlet.function.router
 
 	val route = router {
-		"/person".nest {
+		"/person".nest { // <1>
 			GET("/{id}", accept(APPLICATION_JSON), handler::getPerson)
 			GET(accept(APPLICATION_JSON), handler::listPeople)
 			POST(handler::createPerson)
 		}
 	}
 ----
+<1> Using `nest` DSL.
 
 Though path-based nesting is the most common, you can nest on any kind of predicate by using
 the `nest` method on the builder.