title: Add link to `Add to Calendar` for ics file in erb email
body: <p>I've created a <code>confirmation email</code> using <code>ActionMailer</code> in Rails. My method for creating the email is as follows:</p>
  
  <pre><code>def session_confirmation_email_client(user, coach, date, session_ics, session_outlook, google_cal)
    @google_cal = google_cal
    @user = user
    @date = format_time(date.getlocal)
    @sender = "#{SENDER}"
    mail.attachments["session.ics"] = { mime_type: 'text/calendar', content: session_ics }
    mail(to: user.email, subject: 'Session Confirmation')
  end
  </code></pre>
  
  <p>This properly adds the <code>session.ics</code> attachment to the email but now I want to include an <code>Add To Calendar</code> button which will download the attachment on click.</p>
  
  <p>My erb template for the same looks as follows, at the moment:</p>
  
  <pre><code>&lt;td align="right" valign="top"&gt;
    &lt;%= link_to image_tag("https://s3.amazonaws.com/ical.svg"), LINK_TO_ATTACHMENT %&gt;
  &lt;/td&gt;
  </code></pre>
  
  <p>I'm not sure what link to add over here? Is this way wrong? Basically I'm not sure how to add a download link for an email attachment</p>