The truncator requires Nokogiri to parse out the HTML string.
If you're using Jekyll, add the only_first_p.rb file to your _plugins directory - this will give you the helper only_first_p
as a Liquid filter. In your views, you can use this function in order to show only first paragraph of page/post
page | only_first_p
<p>
{first paragraph content}
</p><a class="readmore" href="{post-url}">Read more</a>
You can choose whether to output a 'Read more' link and the link text to use.
Update your _config.yml as required.
# Only First P Plugin
only_first_p:
show_read_more_link: true
read_more_link_text: 'Read more'
The above is the default configuration and will be used if nothing is specified. Modify as needed.