docs/_includes/read_time.html

{%- unless page.skip_read_time == true -%}
{%- assign words = content | number_of_words -%}
{%- if words >= 360 -%}
<em class="reading-time">Estimated reading time: {{ words | divided_by:180 }} minutes</em>
{%- endif -%}
{%- endunless -%}