Add a note about the ServiceLocator class in the changelog

Author: chalasr

src/Symfony/Component/DependencyInjection/CHANGELOG.md

@@ -10,6 +10,7 @@ CHANGELOG
  * added "container.service_locator" tag for defining service-locator services
  * added anonymous services support in YAML configuration files using the `!service` tag.
  * added "TypedReference" and "ServiceClosureArgument" for creating service-locator services
+ * added `ServiceLocator` - a PSR-11 container holding a set of services to be lazily loaded
  * added "instanceof" section for local interface-defined configs
  * added prototype services for PSR4-based discovery and registration
  * added `ContainerBuilder::getReflectionClass()` for retrieving and tracking reflection class info