Updated filesystem docs on how to use for deeply nested JSON

docs/website/docs/dlt-ecosystem/destinations/filesystem.md

@@ -371,6 +371,14 @@ To configure the layout and placeholders using `config.toml`, use the following
 layout = "{table_name}/{test_placeholder}/{YYYY}-{MM}-{DD}/{ddd}/{mm}/{load_id}.{file_id}.{ext}"
 extra_placeholders = { "test_placeholder" = "test_value" }
 current_datetime="2024-04-14T00:00:00"
+# for deeply nested layouts 
+kwargs = '{"auto_mkdir": true}'
+```
+
+To set using environment variables:
+
+```sh
+export DESTINATION__FILESYSTEM__KWARGS = '{"auto_mkdir": true/false}'
 ```
 
 :::note