Add missed doc contents entry for RSocket chapter

**Cherry-pick to 5.2.x**

(cherry picked from commit 47d7bf3)

Author: artembilan

src/reference/asciidoc/index-single.adoc

@@ -59,6 +59,8 @@ include::./resource.adoc[]
 
 include::./rmi.adoc[]
 
+include::./rsocket.adoc[]
+
 include::./sftp.adoc[]
 
 include::./stomp.adoc[]

src/reference/asciidoc/index.adoc

@@ -38,7 +38,8 @@ as single searchable link:index-single.html[html] and link:../pdf/spring-integra
 <<./mqtt.adoc#mqtt,MQTT Support>> ::
 <<./redis.adoc#redis,Redis Support>> ::
 <<./resource.adoc#resource,Resource Support>> ::
-<<./rmi.adoc#[[rmi,RMI Support>> ::
+<<./rmi.adoc#rmi,RMI Support>> ::
+<<./rsocket.adoc#rsocket,RSocket Support>> ::
 <<./sftp.adoc#sftp,SFTP Adapters>> ::
 <<./stomp.adoc#stomp,STOMP Support>> ::
 <<./stream.adoc#stream,Stream Support>> ::