updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -431,6 +431,7 @@
     * [Test Send File](file_transfer/tests/test_send_file.py)
 
 ## Financial
+  * [Annuity Due Future Value](financial/annuity_due_future_value.py)
   * [Equated Monthly Installments](financial/equated_monthly_installments.py)
   * [Exponential Moving Average](financial/exponential_moving_average.py)
   * [Interest](financial/interest.py)