Hi,
I think the best would be to create a custom field of the table "category" via the menu Display>Custom fields. That way, in the main category (and potentially in sub categories too), you can enter the text you want in the custom field. If you configure the field to display on the frontend, it will appear directly at the top of the categories listing. Then, you can move it at the bottom of the categories listing by editing the category / listing view file via the Display>Views menu.
You should be able to do it by moving the code:
if(!empty($custom_fields_html)){ ?>
<div id="hikashop_category_custom_info_main" class="hikashop_category_custom_info_main">
<h4><?php echo JText::_('CATEGORY_ADDITIONAL_INFORMATION');?></h4>
<table class="hikashop_category_custom_info_main_table">
<?php echo $custom_fields_html; ?>
</table>
</div>
<?php }
after the line:
if(!empty($html)) echo '<div class="hikashop_subcategories_listing">'.$html.'</div>';