Context close docs

- Backport #863
- Relates #866

Author: jvalkeal

spring-shell-docs/src/main/asciidoc/using-shell-customization-contextclose.adoc

@@ -0,0 +1,23 @@
+[[using-shell-customization-contextclose]]
+=== Context Close
+
+Command execution logic happens via Spring Boot's `ApplicationRunner` beans.
+Normally Spring `ApplicationContext` closes automatically after these runner
+beans has been processed unless there is something what keeps it alive like
+use of `@EnableScheduling` or generally speaking there are threads which
+don't die automatically.
+
+It is possible to add configuration property `spring.shell.context.close`
+which registers `ApplicationListener` for `ApplicationReadyEvent` and requests
+context close after shell has completed its execution logic.
+
+[source, yaml]
+----
+spring:
+  shell:
+    context:
+      close: true
+----
+
+NOTE: This setting is not enabled by default.
+

spring-shell-docs/src/main/asciidoc/using-shell-customization.adoc

@@ -10,3 +10,5 @@ include::using-shell-customization-logging.adoc[]
 include::using-shell-customization-commandnotfound.adoc[]
 
 include::using-shell-customization-singlecommand.adoc[]
+
+include::using-shell-customization-contextclose.adoc[]