docs: mention new Service annotation

Author: heitorlessa

docs/core/tracer.md

@@ -58,6 +58,7 @@ You can quickly start by importing the `Tracer` class, initialize it outside the
 When using this `capture_lambda_handler` decorator, Tracer performs these additional tasks to ease operations:
 
 * Creates a `ColdStart` annotation to easily filter traces that have had an initialization overhead
+* Creates a `Service` annotation if `service` parameter or `POWERTOOLS_SERVICE_NAME` is set
 * Captures any response, or full exceptions generated by the handler, and include as tracing metadata
 
 ### Annotations & Metadata