GH-875 - Mention test starter in testing reference documentation chapter.

Author: odrotbohm

src/docs/antora/modules/ROOT/pages/testing.adoc

@@ -2,9 +2,20 @@
 = Integration Testing Application Modules
 
 Spring Modulith allows to run integration tests bootstrapping individual application modules in isolation or combination with others.
-To achieve this, place JUnit test class in an application module package or any sub-package of that and annotate it with `@ApplicationModuleTest`:
+To achieve this, add the Spring Modulith test starter to your project like this
 
-.A application module integration test class
+[source, xml]
+----
+<dependency>
+	<groupId>org.springframework.modulith</groupId>
+	<artifactId>spring-modulith-starter-test</artifactId>
+	<scope>test</scope>
+</dependency>
+----
+
+and place a JUnit test class in an application module package or any sub-package of that and annotate it with `@ApplicationModuleTest`:
+
+.An application module integration test class
 [tabs]
 ======
 Java::
@@ -36,7 +47,7 @@ class OrderIntegrationTests {
 This will run your integration test similar to what `@SpringBootTest` would have achieved but with the bootstrap actually limited to the application module the test resides in.
 If you configure the log level for `org.springframework.modulith` to `DEBUG`, you will see detailed information about how the test execution customizes the Spring Boot bootstrap:
 
-.The log output of a application module integration test bootstrap
+.The log output of an application module integration test bootstrap
 [source, text, subs="macros"]
 ----
   .   ____          _            __ _ _