Fix broken links in guides

Resolves gh-1621

Author: eleftherias

spring-session-docs/src/docs/asciidoc/guides/boot-websocket.adoc

@@ -20,7 +20,7 @@ link:../index.html[Index]
 
 == HttpSession Setup
 
-The first step is to integrate Spring Session with the HttpSession. These steps are already outlined in the link:httpsession.html[HttpSession Guide].
+The first step is to integrate Spring Session with the HttpSession. These steps are already outlined in the link:./boot-redis.html[HttpSession with Redis Guide].
 
 Please make sure you have already integrated Spring Session with HttpSession before proceeding.
 

spring-session-docs/src/docs/asciidoc/guides/java-custom-cookie.adoc

@@ -6,7 +6,7 @@ Rob Winch; Eleftheria Stein-Kousathana
 :docinfodir: guides
 
 This guide describes how to configure Spring Session to use custom cookies with Java Configuration.
-The guide assumes you have already link:./httpsession.html[set up Spring Session in your project].
+The guide assumes you have already set up Spring Session in your project using your chosen data store. For example, link:./boot-redis.html[HttpSession with Redis].
 
 NOTE: You can find the completed guide in the <<custom-cookie-sample, Custom Cookie sample application>>.