[Replicant]

You need to edit the display_Forums_list template and add this code just under the "category-header" code section on or about line 10. You can also add this code to the display_Forums_item template to display the description in the individual forum view. This CSS will also need to be written for the responsive view with @media queries

<tr>
     <td colspan="4"><a class="category-description">{vb:raw channel.description}</a></td>
</tr>

add to css_additional.css, adjust padding, fontsize, and colors as necessary for your taste.

a.category-description {
  background: #F0F0F0;
  float: left;
  color: black!important;
  width: 100%;
}