[Jekyll] How to create post summary in Freshman21 theme

A article post with summary

---
published: true
title: how to create post summary
layout: post
summary: This post show us how to create a post summary step by step. 
author: Yu 
category: howto
tags:
- summary
---

content.

index.html

---
layout: default
---

<div class="home">
  <div class="post">
    
    {% for post in paginator.posts %}
  
    <header class="post-header">
      <h1 class="post-title">
        <a class="post-link" href="{{ post.url | prepend: site.baseurl }}">{{ post.title }}</a>
      </h1>
      <p class="post-meta">
      {{ site.locales[site.default_locale].PostedInCategories }}
      {% for cat in post.categories %}
      <a href="{{site.url}}/categories/#{{ cat }}">{{ cat }}</a>&nbsp;
      {% endfor %}
      {% if post.tags != empty %}
      {{ site.locales[site.default_locale].Taggedwith }}
      {% for tag in post.tags %}
      <a href="{{ site.url }}/tags/#{{ tag }}" title="{{ tag }}">{{ tag }} </a>{% unless post.tags.last == tag %}, {% endunless %}
      {% endfor %}
      {% endif %}
      {{ site.locales[site.default_locale].PostDate }}{{ post.date | date: "%b %-d, %Y" }}
      </p>
    </header>

    <article class="post-content">
      {{ post.summary }}
      <p><a href="{{ post.url | prepend: site.baseurl }}">read more</a></p>
    </article> 
    <hr />
    
    {% endfor %}
  
  </div>
</div>