Update partial date entry documentation based on new default behaviour

guide/C/ch_txns.xml

@@ -216,12 +216,13 @@
     <tip><para>Specifically for dates there's another way you can save time: you can enter
             partial dates. For example if you only enter one number, <application>&app;</application>
             will interpret it as the day in the current month of the current year. If you only enter
-            a day and month, <application>&app;</application> will automatically append the year. By
-            default this is the current year. You can however also configure
-            <application>&app;</application> to take such a date in a sliding window starting
-            a number of months before the current month. This can be done via
+            a day and month, <application>&app;</application> will automatically append the year. The
+            default this to take such a date in a sliding window starting 11 months before the current
+            month. This means that if you enter 1/5 (January 5th) as date while the current date is
+            in December 2015, the date will be completed as 1/5/16. This default can be changed via
             <menuchoice><guimenu>Edit</guimenu><guisubmenu>Preferences</guisubmenu><guisubmenu>Date/Time</guisubmenu>
-            <guilabel>Date Completion</guilabel></menuchoice>.</para></tip>
+            <guilabel>Date Completion</guilabel></menuchoice>. You can change it to either always
+            evaluate a date in the current calendar year or change the start of the sliding window.</para></tip>
 
     <para>In the <guilabel>Num</guilabel> field of the transaction line, you
         can type <keycap>+</keycap> to increment the transaction number from the