Added explanatory note about encodings in imported files.

lang/en_utf8/help/quiz/import.html

@@ -3,6 +3,13 @@
 <p>This function allows you to import questions from 
    external text files, uploaded through a form.  </p>
 
+<p><b>A note about character encodings</b></p>
+
+<p>If your file contains non-ascii characters then you must first convert
+   the file to UTF-8 using your favourite editor or the exporting software 
+   (if the option is available). XML based import formats will be handled
+   automatically provided you are running PHP 5.</p> 
+
 <p>A number of file formats are supported:</p>
 
 <p><b>GIFT format</b></p>