Update getting-started-testing.adoc

Add information abot how to load configuration values inside a `QuarkusTestResourceLifecycleManager`

docs/src/main/asciidoc/getting-started-testing.adoc

@@ -1086,6 +1086,8 @@ but it is common to create custom implementations to address specific applicatio
 Common cases include starting docker containers using https://www.testcontainers.org/[Testcontainers] (an example of which can be found https://github.com/quarkusio/quarkus/blob/main/test-framework/keycloak-server/src/main/java/io/quarkus/test/keycloak/server/KeycloakTestResourceLifecycleManager.java[here]),
 or starting a mock HTTP server using https://wiremock.org/[Wiremock] (an example of which can be found https://github.com/geoand/quarkus-test-demo/blob/main/src/test/java/org/acme/getting/started/country/WiremockCountries.java[here]).
 
+NOTE: As `QuarkusTestResourceLifecycleManager` is not a CDI Bean, classes that implement it can't have fields injected with `@Inject`. You can use `String propertyName = ConfigProvider.getConfig().getValue("quarkus.my-config-group.myconfig", String.class);`
+
 
 === Altering the test class
 When creating a custom `QuarkusTestResourceLifecycleManager` that needs to inject the something into the test class, the `inject` methods can be used.