Adding clarity on permissions when using the same user from destination

Author: charholt

src/connections/reverse-etl/reverse-etl-source-setup-guides/postgres-setup.md

@@ -40,4 +40,10 @@ To set up Postgres with Reverse ETL:
 
 * Give the `segment` user write permissions for the Segment managed schema (`__SEGMENT_REVERSE_ETL`), which keeps track of changes to the query results.  
 
-After you've successfully added your Postgres source, [add a model](/docs/connections/reverse-etl/setup/#step-2-add-a-model) and follow the rest of the steps in the Reverse ETL setup guide.
+After you've successfully added your Postgres source, [add a model](/docs/connections/reverse-etl/setup/#step-2-add-a-model) and follow the rest of the steps in the Reverse ETL setup guide.
+
+### Using the Same User for a Postgres Destination and Reverse ETL?
+If you’re using the same database user for both a Segment Postgres warehouse destination (where Segment writes data into Postgres) and Reverse ETL (where Segment reads from Postgres), make sure the user has:
+- SELECT or READ access on all source tables for Reverse ETL
+- CREATE SCHEMA `__SEGMENT_REVERSE_ETL` permission (or ability to use an existing schema)
+- INSERT, UPDATE, and DELETE permissions on tables within `__SEGMENT_REVERSE_ETL`