Example code for a 'related links' include.

README.md

#Usage Use the below code to include a post from your posts with a title of "Hello World!" You can change the collection that the include uses instead of using posts.

{% include related.html item="Hello World!" collection=site.posts %}

Could also be changed to match a custom variable instead of title if name collisions are a concern.

post.md

layout	title	date	categories
post	Test content	2016-02-25 19:30:21 +1100	hello

test content

{% include related.html item="Hello World!" collection=site.posts %}

related.html

{% for p in include.collection %}
    {% if p.title == include.item %}
<a href="{{ site.url/p.url }}">{{ p.title }}<a>
    {% endif %}
{% endfor %}