update doc

Author: sycai

bigframes/operations/output_schemas.py

@@ -30,6 +30,7 @@ def parse_sql_fields(sql: str) -> tuple[pa.Field]:
 
     Examples:
         "x INT64, y FLOAT64" => (pa.field("x", pa.int64()), pa.field("y", pa.float64()))
+        "y INT64, x FLOAT64" => (pa.field("x", pa.float64()), pa.field("y", pa.int64()))
     """
     sg_type = sqlglot.parse_one(f"STRUCT<{sql}>", read="bigquery")
     pa_struct = _sg_to_pyarrow_dtype(cast(sgexp.DataType, sg_type))