Add information about delete records id

Author: Olesia

src/connections/reverse-etl/index.md

@@ -178,6 +178,9 @@ To get started with using Reverse ETL for subscriptions:
 ## Record diffing
 Reverse ETL computes the incremental changes to your data directly within your data warehouse. The Unique Identifier column is used to detect the data changes, such as new, updated, and deleted records.
 
+> info "Delete Records Payload"
+> The only value passed for deleted records is its unique id which can be accessed as __segment_id. 
+
 In order for Segment to compute the data changes within your warehouse, Segment needs to have both read and write permissions to the warehouse schema table. At a high level, the extract process requires read permissions for the query being executed. Segment keeps track of changes to the query results through tables that Segment manages in a dedicated schema (for example, `_segment_reverse_etl`), which requires some write permissions.
 
 > warning ""