Fix for issue #3848

Added the content that didn't get carried forward from 4.2.x.

Author: Jay Bryant

spring-batch-docs/src/main/asciidoc/job.adoc

@@ -438,6 +438,27 @@ created in addition to a number of beans made available to be autowired:
 The core interface for this configuration is the `BatchConfigurer`. The default
 implementation provides the beans mentioned above and requires a `DataSource` as a bean
 within the context to be provided. This data source is used by the JobRepository.
+You can customize any of these beans
+by creating a custom implementation of the `BatchConfigurer` interface.
+Typically, extending the `DefaultBatchConfigurer` (which is provided if a
+`BatchConfigurer` is not found) and overriding the required getter is sufficient.
+However, implementing your own from scratch may be required. The following
+example shows how to provide a custom transaction manager:
+
+====
+[source, java]
+----
+@Bean
+public BatchConfigurer batchConfigurer() {
+	return new DefaultBatchConfigurer() {
+		@Override
+		public PlatformTransactionManager getTransactionManager() {
+			return new MyTransactionManager();
+		}
+	};
+}
+----
+====
 
 [NOTE]
 ====