Add shared calendar to the wiki

[hamishwillee]

Need shared calendar here: https://wiki.dronecode.org/start

The iframe to display is here:

<iframe src="https://calendar.google.com/calendar/embed?src=linuxfoundation.org_g3uvkjblququ0ac3kdvj1j5mhs%40group.calendar.google.com&ctz=America/Los_Angeles" style="border: 0" width="800" height="600" frameborder="0" scrolling="no"></iframe>

The calendar support in wiki appears not to work. Have requested a solution that will.