Merge pull request #6509 from segmentio/charholt-patch-1

Update index.md

Author: forstisabella

src/connections/reverse-etl/index.md

@@ -64,6 +64,7 @@ To add your first model:
 4. Choose a column to use as the unique identifier for each record in the **Unique Identifier column** field.
     * The Unique Identifier should be a column with unique values per record to ensure checkpointing works as expected. It can potentially be a primary key. This column is used to detect new, updated, and deleted records.
 5. Click **Preview** to see a preview of the results of your SQL query. The data from the preview is extracted from the first 10 records of your warehouse.
+    * Segment caches preview queries and result sets in the UI, and stores the preview cache at the source level. If you make two queries for the same source, Segment returns identical preview results. However, during the next synchronization, the latest data will be sent to the connected destinations.
 6. Click **Next**.
 7. Enter your **Model Name**.
 8. Click **Create Model**.