Clarify handling and binding or YAML lists

The docs related to YAML lists were out of date and
lacked an example making it clear how to bind to them.

See gh-501

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

@@ -372,25 +372,39 @@ Would be transformed into these properties:
 	environments.prod.name=My Cool App
 ----
 
-YAML lists are represented as comma-separated values (useful for simple String values)
-and also as property keys with `[index]` dereferencers, for example this YAML:
+YAML lists are represented as property keys with `[index]` dereferencers, 
+for example this YAML:
 
 [source,yaml,indent=0]
 ----
-	 servers:
- 		- dev.bar.com
- 		- foo.bar.com
+	 my:
+        servers:
+ 		    - dev.bar.com
+ 		    - foo.bar.com
 ----
 
 Would be transformed into these properties:
 
 [source,properties,indent=0]
 ----
-	servers=dev.bar.com,foo.bar.com
-	servers[0]=dev.bar.com
-	servers[1]=foo.bar.com
+	my.servers[0]=dev.bar.com
+	my.servers[1]=foo.bar.com
 ----
 
+To bind to properties like that using the Spring `DataBinder`
+utilities (which is what `@ConfigurationProperties` does) you need to
+have a property in the target bean of type `java.util.List` (or `Set`)
+and you either need to provide a setter, or initialize it with a
+mutable value, e.g. this will bind to the properties above
+
+[source,java,indent=0]
+----
+@ConfigurationProperties(prefix="my")
+public class Config {
+    private List<String> servers = new ArrayList<String>();
+    public List<String> getServers() { return this.servers; }
+}
+----
 
 
 [[boot-features-external-config-exposing-yaml-to-spring]]