Update contributor doc with additional meetings
Update contributor doc with additional meetings

We've recently formalized some of the extra meetings we've been
having (for example, I325a998983dc and I16aceb82ba4f), so add them
to the new contributor doc.

Change-Id: Ic9befbd5e5f1740ce9725bbedd8695324d4c0b6f

openstack/cinder,openstack/cinder,mahak/cinder,mahak/cinder