Add dependency management for spock-spring and document its use

Closes #1234

spring-boot-dependencies/pom.xml

@@ -949,6 +949,11 @@
 					</exclusion>
 				</exclusions>
 			</dependency>
+			<dependency>
+				<groupId>org.spockframework</groupId>
+				<artifactId>spock-spring</artifactId>
+				<version>${spock.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.springframework</groupId>
 				<artifactId>spring-framework-bom</artifactId>

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

@@ -2005,8 +2005,11 @@ 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
+If you wish to use Spock to test a Spring Boot application you should add a dependency
+on Spock's `spock-spring` module to your application's build. `spock-spring` integrates
+Spring's test framework into Spock.
+
+Please note that 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