Overview
We can iterate over site.tags
, each item is an array with two elements. The first element in the array is the tag name, the second element is a list of the posts in that tag.
...
{% for tag in site.tags %}
<h2>{{ tag[0] }}</h2>
<ul>
{% for post in tag[1] %}
<li><a href="{{ post.url }}">{{ post.title }}</a></li>
{% endfor %}
</ul>
{% endfor %}
...