docs: enhance file_sort_order documentation in SessionContext

Author: kosiew

python/datafusion/context.py

@@ -567,7 +567,9 @@ def register_listing_table(
             table_partition_cols: Partition columns.
             file_extension: File extension of the provided table.
             schema: The data source schema.
-            file_sort_order: Sort order for the file.
+            file_sort_order: Sort order for the file. Each sort key can be
+                specified as a column name (``str``), an expression
+                (``Expr``), or a ``SortExpr``.
         """
         if table_partition_cols is None:
             table_partition_cols = []
@@ -822,7 +824,9 @@ def register_parquet(
                 that may be in the file schema. This can help avoid schema
                 conflicts due to metadata.
             schema: The data source schema.
-            file_sort_order: Sort order for the file.
+            file_sort_order: Sort order for the file. Each sort key can be
+                specified as a column name (``str``), an expression
+                (``Expr``), or a ``SortExpr``.
         """
         if table_partition_cols is None:
             table_partition_cols = []
@@ -1109,7 +1113,9 @@ def read_parquet(
             schema: An optional schema representing the parquet files. If None,
                 the parquet reader will try to infer it based on data in the
                 file.
-            file_sort_order: Sort order for the file.
+            file_sort_order: Sort order for the file. Each sort key can be
+                specified as a column name (``str``), an expression
+                (``Expr``), or a ``SortExpr``.
 
         Returns:
             DataFrame representation of the read Parquet files