Document better ASYNC dispatch type config for Filters

Although the need to map the ASYNC dispatcher type to a Filter was
already mentioned, it wasn't very prominent and can be quite critical
in some cases. This change addresses that.

Issue: SPR-10440

Author: rstoyanchev

src/asciidoc/index.adoc

@@ -29960,7 +29960,8 @@ To use Servlet 3 async request processing, you need to update `web.xml` to versi
 ----
 	<web-app xmlns="http://java.sun.com/xml/ns/javaee"
 		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-		xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
+				http://java.sun.com/xml/ns/javaee
+				http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
 		version="3.0">
 
 		...
@@ -29975,6 +29976,43 @@ ASYNC dispatcher type. Note that it is safe to enable the ASYNC dispatcher type
 filters provided with the Spring Framework since they will not get involved in async
 dispatches unless needed.
 
+[WARNING]
+====
+Note that for some Filters it is absolutely critical to ensure they are mapped to
+be invoked during asynchronous dispatches. For example if a filter such as the
+`OpenEntityManagerInViewFilter` is responsible for releasing database connection
+resources and must be invoked at the end of an async request.
+
+Below is an example of a propertly configured filter:
+====
+
+[source,xml,indent=0]
+[subs="verbatim,quotes"]
+----
+	<web-app xmlns="http://java.sun.com/xml/ns/javaee"
+		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		xsi:schemaLocation="
+				http://java.sun.com/xml/ns/javaee
+				http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
+		version="3.0">
+
+		<filter>
+			<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
+			<filter-class>org.springframework.~.OpenEntityManagerInViewFilter</filter-class>
+			<async-supported>true</async-supported>
+		</filter>
+
+		<filter-mapping>
+			<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
+			<url-pattern>/*</url-pattern>
+			<dispatcher>REQUEST</dispatcher>
+			<dispatcher>ASYNC</dispatcher>
+		</filter-mapping>
+
+	</web-app>
+
+----
+
 If using Servlet 3, Java based configuration, e.g. via `WebApplicationInitializer`,
 you'll also need to set the "asyncSupported" flag as well as the ASYNC dispatcher type
 just like with `web.xml`. To simplify all this configuration, consider extending