site/_includes/custom/mydoc/getting_started_series_next.html

<p>{% assign series_pages = site.tags.series_acme %}
    {% for p in pages %}
    {% if p.series == "Getting Started" %}
    {% assign nextTopic = page.weight | plus: "1"  %}
    {% if p.weight == nextTopic  %}
    <a href="{{p.url | prepend: '..'}}"><button type="button" class="btn btn-primary">Next: {{p.title}}</button></a>
    {% endif %}
    {% endif %}
    {% endfor %}
</p>