Add missing WebFlux CORS Reference

Closes gh-9951

Author: eleftherias

docs/manual/src/docs/asciidoc/_includes/reactive/cors.adoc

@@ -1,6 +1,6 @@
 
 [[webflux-cors]]
-== CORS
+= CORS
 
 Spring Framework provides https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html#webflux-cors-intro[first class support for CORS].
 CORS must be processed before Spring Security because the pre-flight request will not contain any cookies (i.e. the `JSESSIONID`).

docs/manual/src/docs/asciidoc/_includes/reactive/index.adoc

@@ -14,6 +14,8 @@ include::webclient.adoc[leveloffset=+1]
 
 include::method.adoc[leveloffset=+1]
 
+include::cors.adoc[leveloffset=+1]
+
 include::test.adoc[leveloffset=+1]
 
 include::rsocket.adoc[leveloffset=+1]