Bug 769746 - Zero interest loan formula fails.

Document that the Mortgage Assistant doesn't support 0-interest loans.
Provide instruction for creating a zero-interest loan repayment
as a simple scheduled transaction.

help/C/Help_ch_Tools_Assistants.xml

@@ -2330,7 +2330,8 @@
            a scheduled transaction, the assistant creates a variable formula so that the
            compounding interest is correctly calculated. To start this assistant manually go to
            <menuchoice><guilabel>Actions</guilabel><guisubmenu>Scheduled Transactions</guisubmenu>
-           <guimenuitem>Mortgage and Loan Repayment...</guimenuitem></menuchoice>.</para>
+          <guimenuitem>Mortgage and Loan Repayment...</guimenuitem></menuchoice>.</para>
+          <para>It does not support zero-interest loans, but one doesn't really need an assistant for that: Just create a scheduled transaction for the principal divided by the number of payments that lasts for the number of payments. For example, if one has borrowed $1200 for a year at no interest and promised to pay it back in monthly installments, the repayment schedule is $100 monthly for twelve months.</para>
 
           <para>The Mortgage and Loan Repayment assistant opens with a screen that briefly
            describes what this assistant does. The three buttons at the very bottom of the screen
@@ -2370,7 +2371,7 @@
             </listitem>
 
             <listitem>
-              <para><guilabel>Interest Rate:</guilabel> Enter the loan interest rate.</para>
+              <para><guilabel>Interest Rate:</guilabel> Enter the loan interest rate in percent per compounding period. The Assistant supports rates between .001% and 100%.</para>
             </listitem>
 
             <listitem>