docs: note that incremental-refresh bounds follow the session time zone

For a timestamp with time zone column, Power BI sends RangeStart and
RangeEnd as plain TIMESTAMP literals, which Trino interprets in the
session time zone. Partition boundaries therefore move if TimeZone
changes on a dataset that already has partitions.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: adwk67

README.md

@@ -78,6 +78,11 @@ proper entry in the **Get Data** dialog instead of the generic ODBC one.
 2. In **File > Options > Security**, allow any extension to load.
 3. Restart Power BI Desktop. **Stackable Trino** now appears under **Get Data**.
 
+For incremental refresh on a `timestamp with time zone` column, Trino compares
+the `RangeStart` and `RangeEnd` bounds in the session time zone (`TimeZone`),
+so partition boundaries follow that zone. Changing `TimeZone` on a dataset that
+already has partitions moves the boundaries.
+
 ### Your first query
 
 Assuming a Trino instance is reachable on the given host and port: