Add documentation about using list of objects in @ConfigProperties

Related to: quarkusio#14006

docs/src/main/asciidoc/config-reference.adoc

@@ -310,6 +310,51 @@ public class SomeBean {
 <1> At this injection point `greetingConfiguration` will use the `greeting` prefix since that is what has been defined on `@ConfigProperties`.
 <2> At this injection point `otherConfiguration` will use the `other` prefix from `@ConfigPrefix` instead of the `greeting` prefix. Notice that in this case `@Inject` is not required.
 
+=== Using a list of objects
+
+In certain cases it might be necessary to support complex configuration structures that utilize a list of objects as shown in the following example:
+
+`ComplexConfiguration.java`
+[source,java]
+----
+@ConfigProperties(prefix = "complex")
+public class ComplexConfiguration {
+    public String name;
+    public String user;
+    public String password;
+    public List<Nested> inputs;
+    public List<Nested> outputs;
+
+    public static class Nested {
+        public String user;
+        public String password;
+    }
+}
+----
+
+`@ConfigProperties` can only support such use cases when the `quarkus-config-yaml` extension is present. A corresponding example YAML configuration could be:
+
+`application.yaml`
+[source,yaml]
+----
+complex:
+  name: defaultName
+  user: defaultUser
+  password: defaultPassword
+  inputs:
+    - user: user
+      password: secret
+    - user: otheruser
+      password: secret2
+  outputs:
+    - user: someuser
+      password: asecret
+    - user: someotheruser
+      password: anothersecret
+----
+
+WARNING: A limitation of such configuration is that the types used as the generic types of the lists need to be classes and not interfaces.
+
 [[configuration_profiles]]
 == Configuration Profiles