Custom menus in Jekyll

_config.yml

header_menu:
  About: "/about"
  Departments: "/departments"
  Contact: "/people"

header_menu.html

<ul>
  {% for item in site.header_menu %}
    {% assign title = item.first %}
    {% assign link = item.last %}
    <li>
      <a href="{{ link }}">
        {{ title }}
      </a>
    </li>
  {% endfor %}
</ul>