(DOCSP-16173) Clarify storage charges (#170)

* (DOCSP-16173) Clarify Data Lake storage charges

Author: zach-carr

source/index.txt

@@ -99,8 +99,11 @@ regions:
 Billing
 -------
 
-|service| |data-lake| incurs costs for the amount of data processed and
-returned by the service.
+You incur |service| |data-lake| costs for the following:
+
+- storage on the cloud object storage,
+- data scanned by |data-lake|, and
+- data returned by |data-lake|.
 
 Total Data Processed
 ~~~~~~~~~~~~~~~~~~~~