add db2 to supported retl sources

Author: gilsegment

src/connections/reverse-etl/setup.md

@@ -28,6 +28,7 @@ To add your warehouse as a source:
   - [Azure Reverse ETL setup guide](/docs/connections/reverse-etl/reverse-etl-source-setup-guides/azure-setup)
   - [BigQuery Reverse ETL setup guide](/docs/connections/reverse-etl/reverse-etl-source-setup-guides/bigquery-setup)
   - [Databricks Reverse ETL setup guide](/docs/connections/reverse-etl/reverse-etl-source-setup-guides/databricks-setup)
+  - [DB2 Reverse ETL setup guide](/docs/connections/reverse-etl/reverse-etl-source-setup-guides/db2-setup)
   - [Postgres Reverse ETL setup guide](/docs/connections/reverse-etl/reverse-etl-source-setup-guides/postgres-setup)
   - [Redshift Reverse ETL setup guide](/docs/connections/reverse-etl/reverse-etl-source-setup-guides/redshift-setup)
   - [Snowflake Reverse ETL setup guide](/docs/connections/reverse-etl/reverse-etl-source-setup-guides/snowflake-setup)