Update duckdb.md (#293)

* Update duckdb.md

* Update duckdb.md

spiceaidocs/docs/data-connectors/duckdb.md

@@ -58,6 +58,7 @@ datasets:
     params:
       open: path/to/duckdb_function_file.duckdb
 ```
+Note: For DuckDB functions, `params.open` is still required.
 
 Datasets created from DuckDB functions are similar to a standard `SELECT` query. For example: