feat: add description section to section/term/taxonomies, fix header margin

layouts/_default/term.html

@@ -9,6 +9,9 @@
     {{partial "header.html" .}}
     <article>
         <h1>Tag: {{ .Title }}</h1>
+        {{with .Params.description}}
+            <p>{{.}}</p>
+        {{end}}
         {{partial "page-list.html" .Paginator.Pages}}
         {{ template "_internal/pagination.html" . }}
     </article>