Added documentation for es cleaner job (#491)

Signed-off-by: Cristiano Belisario Fontes <[email protected]>

README.adoc

@@ -311,6 +311,21 @@ The self-provision of an Elasticsearch cluster can be disabled by setting the fl
 
 IMPORTANT: At the moment there can be only one Jaeger with self-provisioned Elasticsearch instance per namespace.
 
+=== Elasticsearch index cleaner job
+
+When using `elasticsearch` storage by default a job is created to clean old traces from it, the options for it are listed below so you can configure it to your use case
+
+[source,yaml]
+-----
+storage:
+  type: elasticsearch
+  esIndexCleaner:
+    enabled: false                                // turn the job deployment on and off
+    numberOfDays: 7                               // number of days to wait before deleting a record
+    schedule: "55 23 * * *"                       // cron expression for it to run
+    image: jaegertracing/jaeger-es-index-cleaner  // image of the job
+-----
+
 == Accessing the UI
 
 === Kubernetes