add model on bond index schedule repayment

Author: yellowbean

docs/source/modeling.rst

@@ -2144,6 +2144,8 @@ BalanceByPeriod
 
 .. versionadded:: 0.42.0
 
+The repayment schedule balance depends on waterfall distribution periods( defined by `PayFreq` in deal dates )
+
 .. code-block:: python
 
     ("A1",{"balance":1000
@@ -2161,6 +2163,12 @@ BalanceByPeriod
             })
 
 
+.. warning::
+    
+    If a deal is already ongoing , make sure need to model `bond paied period` in `deal states`
+
+
+
 Lockout
 """""""""""""
 A bond with ``Lockout`` type is used to setup bond with only recieve principal after the `lockout date`