I just looked at this since I assumed that categories would have meta descriptions, and for some reason they are not added. So I've just added it to Q2A!
If you want to implement it yourself you can do so by adding this code to the qa_q_list_page_content function in qa-include/app/q-list.php:
// set meta description on category pages
if (!empty($navcategories[$categoryid]['content'])) {
$qa_content['description'] = qa_html($navcategories[$categoryid]['content']);
}
The link above may help if you're not sure where to put it.
