hugo-coder/layouts/_default/_markup/render-heading.html

<h{{ .Level }} id="{{ .Anchor | safeURL }}">
  {{ .Text | safeHTML }}
  <a class="heading-link" href="#{{ .Anchor | safeURL }}">
    <i class="fa fa-link" aria-hidden="true" title="{{ i18n "link_to_heading" | default "Link to heading" }}"></i>
    <span class="sr-only">{{ i18n "link_to_heading" | default "Link to heading" }}</span>
  </a>
</h{{ .Level }}>