In Calendar, tap Calendars > Add Calendar > Add Subscription Calendar.

Enter the follwing web address, then tap Subscribe.
https://calendar.google.com/calendar/ical/referee%40hkrugby.com/public/basic.ics

Click Add.

Go to https://calendar.google.com through a browser, login to Google Calendar with the Google Account used for synchronising the mobile device.

In "Desktop" view of Google Calendar, click the "+" sign beside “Other calendars” on the left hand side of the Google Calendar.

Select “From URL”.

Enter the URL below:
https://calendar.google.com/calendar/ical/referee%40hkrugby.com/public/basic.ics

Click “Add Calendar” and the subscription will be completed on Google Calendar.

In the mobile device, Tap "Settings" on the Home screen.

Select the Google account used for synchronizing your mobile device and sync with the calendar app.