<header class="post-header">
  {{ if .Params.thumbnail }}
    <div class="post-avatar-wrapper">
      <img class="post-avatar" alt="" src="{{ .Params.thumbnail }}">
    </div>
  {{ end }}
  <h1 class="post-title">
    <a href="{{ .RelPermalink }}">
      {{ if .Draft }}
        <span class="draft-marker">{draft}</span>
      {{ end }}
      {{ .Title }}
    </a>
  </h1>
</header>

<header class="post-header">
  {{ if .Params.thumbnail }}
    <div class="post-avatar-wrapper">
      <img class="post-avatar" alt="" src="{{ .Params.thumbnail }}">
    </div>
  {{ end }}
  <h1 class="post-title">
    <a href="{{ .RelPermalink }}">
      {{ if .Draft }}
        <span class="draft-marker">{draft}</span>
      {{ end }}
      {{ .Title }}
    </a>
  </h1>
  <h3 class="post-subtitle">
    {{ .Params.subtitle }}
  </h3>
</header>

Add subtitle in post list
Add subtitle in post list

Why:
To enable subtitle in post list

This change addresses the need by:
Adding the code to show subtitle
in `partials/post-header.html`

This change affects the following:
