Sticky post in GitHub Page using plugin

I want to have a post that will remain the first post on the page even when newer posts are created. I found this plugin

but i dont know what to write in etc in

{% assign sorted = paginator.posts | sort: "stickiness" %}
{% for post in sorted %}
{% endfor %}

Also should I add to _config.yml

# Gems
  - jekyll-stickyposts

The theme I’m using is Lanyon theme. My webpage can be found here