Merge pull request #13061 from vpavic:improve-docs

* pr/13061:
  Polish "Improve Spring Session docs"
  Improve Spring Session docs

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

@@ -5994,9 +5994,10 @@ When building a reactive web application, the following stores can be auto-confi
 * Redis
 * MongoDB
 
-If Spring Session is available, you must choose the
-{sc-spring-boot-autoconfigure}/session/StoreType.{sc-ext}[`StoreType`] that you wish to
-use to store the sessions. For instance, to use JDBC as the back-end store, you can
+If a single Spring Session module is present on the classpath, Spring Boot uses that store
+implementation automatically. If you have more than one implementation, you must choose
+the {sc-spring-boot-autoconfigure}/session/StoreType.{sc-ext}[`StoreType`] that you wish
+to use to store the sessions. For instance, to use JDBC as the back-end store, you can
 configure your application as follows:
 
 [source,properties,indent=0]