Minor polishing on message converter doc

This fixes #616

Add example for MessageConverter

spring-cloud-stream-core-docs/src/main/asciidoc/spring-cloud-stream-overview.adoc

@@ -1007,7 +1007,7 @@ Spring Cloud Stream can handle messages based on this information in two ways:
 * Through its `contentType` settings on inbound and outbound channels
 * Through its argument mapping performed for methods annotated with `@StreamListener`
 
-Spring Cloud Stream allows you to declaratively configure type conversion for inputs and outputs using the `content-type` property of a binding.
+Spring Cloud Stream allows you to declaratively configure type conversion for inputs and outputs using the `spring.cloud.stream.bindngs.<channelName>.content-type` property of a binding.
 Note that general type conversion may also be accomplished easily by using a transformer inside your application.
 Currently, Spring Cloud Stream natively supports the following type conversions commonly used in streams:
 
@@ -1106,7 +1106,48 @@ For the conversion of inbound messages, especially when the target is a POJO, th
 
 Besides the conversions that it supports out of the box, Spring Cloud Stream also supports registering your own message conversion implementations.
 This allows you to send and receive data in a variety of custom formats, including binary, and associate them with specific `contentTypes`.
-In order to do so, you can create a class that extends `AbstractMessageConverter`
+Spring Cloud Stream registers all the beans of type `org.springframework.messaging.converter.MessageConverter` as custom message converters along with the out of the box message converters.
+
+If your message converter needs to work with specific `content-type` and the target class (for both input and output), then the message converter needs to extend `org.springframework.messaging.converter.AbstractMessageConverter`.
+For the conversion using @StreamListener, the message converter that implements `org.springframework.messaging.converter.MessageConverter` would be suffice.
+
+Here is an example of creating a message converter bean (with the content-type application/bar) inside the Spring Cloud Stream application:
+
+[source,java]
+----
+@EnableBinding(Sink.class)
+@SpringBootApplication
+public static class SinkApplication {
+
+  ...
+
+  @Bean
+  public MessageConverter customMessageConverter() {
+    return new MyCustomMessageConverter();
+  }
+----
+
+[source,java]
+----
+
+public class MyCustomMessageConverter extends AbstractMessageConverter {
+
+	public MyCustomMessageConverter() {
+		super(new MimeType("application", "bar"));
+	}
+
+	@Override
+    protected boolean supports(Class<?> clazz) {
+        return (Bar.class == clazz);
+    }
+
+	@Override
+	protected Object convertFromInternal(Message<?> message, Class<?> targetClass, Object conversionHint) {
+		Object payload = message.getPayload();
+		return (payload instanceof Bar ? payload : new Bar((byte[]) payload));
+	}
+}
+----
 
 === Schema-based message converters
 
@@ -1127,7 +1168,7 @@ If the target type of the conversion is a `GenericRecord`, then a schema must be
 
 For using it, you can simply add it to the application context, optionally specifying one ore more `MimeTypes` to associate it with.
 The default `MimeType` is `application/avro`.
-Here is an example of configuring it in a processor application registering the Apache Avro, without a predefined schema:
+Here is an example of configuring it in a sink application registering the Apache Avro MessageConverter, without a predefined schema:
 
 [source,java]
 ----