Add some documentation for contest filter function

help/h23.html

@@ -50,15 +50,26 @@ the time span (<b>date from-to</b>) to make the <b>Membership</b> option active.
 Pressing calendar icon is easy way to set date. Double click on selected date closes calendar and sets the date. Pressing ESC closes calendar, but does not set date. Date can also be typed in manually.
 <br><br>
 <img src="img/h101b.png"><br><br>
-The sorting order can be selected from the following options:<<br>
+The sorting order can be selected from the following options:<br>
 <img src="img/h50.png"><br><br>
 Selected records can be grouped by the following criteria:<br>
 <img src="img/h51.png"><br><br>
 Once your filter is set up, go to the upper menu (item 'File' in QSO list) and choose
 'Export'.<br>
-<img src="img/h45.png"<br><br>
+<img src="img/h45.png"><br><br>
 Choose 'ADIF' or 'HTML'. The usual File Save dialog appears (depending on the desktop
-used). Choose a location and file name.<br>
+used). Choose a location and file name.<br><br>
+
+<a name="cfil"><h3>Contest Filter</h3></a>
+Besides the standard filter function there is a separate menu for filtering QSOs based on contests. 
+To use this please select "Contest filter" from the "Filter"-menu.<br><br>
+<img src="img/h45h.png"><br><br>
+The function autmatically loads the names of all contests that QSO where logged in in the QSO database.
+You can then choose based on the name of the contest which QSOs to show and the export accordingly.
+It is recommended to use individual names for the contests e.g. extend by month and year to be able 
+to distinguish.<br><br>
+<img src="img/h45i.png"><br><br>
+
 <p align=center><img src=img/line.png></p>
 <table style="text-align: left; width: 100%;" border="0" cellpadding="2" cellspacing="2">
     <tbody>