docs: Add documentation for Iceberg transaction support

presto-docs/src/main/sphinx/connector/iceberg.rst

@@ -1926,6 +1926,37 @@ Iceberg tables do not support running multiple :doc:`../sql/merge` statements on
     Failed to commit Iceberg update to table: <table name>
     Found conflicting files that can contain records matching true
 
+Transaction support
+^^^^^^^^^^^^^^^^^^^
+
+The Iceberg connector supports explicit multi-statement transactions with writes
+to a single Iceberg table. To run transaction statements, use
+:doc:`/sql/start-transaction` with :doc:`/sql/commit` or :doc:`/sql/rollback`.
+
+The Iceberg connector provides snapshot isolation at ``REPEATABLE READ`` level.
+This also satisfies ``READ COMMITTED`` and ``READ UNCOMMITTED``, so these
+isolation levels are supported as well. For snapshot semantics, use
+``REPEATABLE READ``::
+
+    START TRANSACTION ISOLATION LEVEL REPEATABLE READ;
+    INSERT INTO iceberg.default.test_table (id, status) VALUES (1, 'pending');
+    UPDATE iceberg.default.test_table SET status = 'committed' WHERE id = 1;
+    COMMIT;
+
+Limitations:
+
+* Writes in the same transaction can target only one Iceberg table. Attempts
+  to write to another table fail with ``Not allowed to open write transactions on multiple tables``.
+* ``SERIALIZABLE`` isolation is not supported by the Iceberg connector.
+* The following statements are only supported in autocommit mode:
+  ``MERGE INTO``, ``CREATE/DROP/RENAME TABLE``,
+  ``CREATE/DROP/RENAME SCHEMA``, ``CREATE/DROP/RENAME VIEW``,
+  ``CREATE/DROP/REFRESH MATERIALIZED VIEW``, ``TRUNCATE TABLE``, and
+  ``ANALYZE``.
+* ``CALL`` statements are only supported in autocommit mode.
+* If concurrent transactions change table metadata, commit may fail and require
+  retrying the transaction (for example, ``Table metadata refresh is required``).
+
 .. _iceberg_analyze:
 
 Collecting table and column statistics