Use article element more appropriately on bug page

Timeline

Amolith opened

Every git-bug has a title, but there might not be an initial comment. Subsequent comments don't have titles.

<article>
  {{if not comment}}
  <header>Title</header>
  {{end}}
  {{if description}}Description{{end}}
  <footer>Author <time datetime="{{.Data | rfc3339}}">{{.CreatedAt | formatDate}}</time></footer>
</article>

Amolith closed the bug

Amolith closed the bug