Add Description to single taxonomy list

Having a description for each post just like `blog_list.html` adds more uniformity and is very helpful

templates/taxonomy_single.html

@@ -14,6 +14,9 @@
       {{ page.title }}
     </a>
   </h3>
+  {%- if page.description %}
+    <p>{{ page.description }}</p>
+  {%- endif %}
   <small>
     <time datetime='{{ page.date | date(format='%+') }}' pubdate>
       {{- page.date | date(format=config.extra.date_format) -}}