Document need to use @ContextConfiguration with Spock

Closes spring-projects#1167

Author: wilkinsona

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

@@ -2000,6 +2000,27 @@ in order to run your integration tests using random ports. For example:
 See <<howto-discover-the-http-port-at-runtime>> for a description of how you can discover
 the actual port that was allocated for the duration of the tests.
 
+[[boot-features-testing-spring-boot-applications-with-spock]]
+==== Using Spock to test Spring Boot applications
+
+If you wish to use Spock to test a Spring Boot application then you cannot use the
+`@SpringApplicationConfiguration` annotation that was
+<<boot-features-testing-spring-boot-applications,described above>> as Spock
+https://code.google.com/p/spock/issues/detail?id=349[does not find the
+`@ContextConfiguration` meta-annotation]. To work around
+this limitation, you should use the `@ContextConfiguration` annotation directly and
+configure it to use the Spring Boot-specfic context loader:
+
+[source,groovy,indent=0]
+----
+	@ContextConfiguration(loader = SpringApplicationContextLoader.class)
+	class ExampleSpec extends Specification {
+
+		// ...
+
+	}
+----
+
 
 
 [[boot-features-test-utilities]]