Clarify default value of ConditionalOnMissingBean on bean methods

Closes gh-9387

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

@@ -6231,6 +6231,24 @@ attribute to specify beans by type, or `name` to specify beans by name. The `sea
 attribute allows you to limit the `ApplicationContext` hierarchy that should be considered
 when searching for beans.
 
+When placed on a `@Bean` method, the target type defaults to the return type of the
+method, for instance:
+
+[source,java,indent=0]
+----
+	@Configuration
+	public class MyAutoConfiguration {
+
+		@Bean
+		@ConditionalOnMissingBean
+		public MyService myService() { ... }
+
+	}
+----
+
+In the example above, the `myService` bean is going to be created if no bean of type
+`MyService` is already contained in the `ApplicationContext`.
+
 TIP: You need to be very careful about the order that bean definitions are added as these
 conditions are evaluated based on what has been processed so far. For this reason,
 we recommend only using `@ConditionalOnBean` and `@ConditionalOnMissingBean` annotations