add link for ics
<dialog class="mdl-dialog dialog-calendar">
<h4 class="mdl-dialog__title">Bangumi Calendar</h4>
<div class="mdl-dialog__content">
+ <a class="mdl-color-text--blue-grey-400" target="_blank" href="/calendar.ics">ICS Calendar for iOS / Android</a>
<p>
{% for i, v in enumerate(cal.items()) %}
<h5 class="{% if i == 0 %}strong{% end %}">{{ v[0] }}.</h5>
