Each time you make a new Google Calendar event, this applet adds a new task at that time with that description to Todoist. (Unfortunately, does not add existing GCal events or sync changes.) Yes, Todoist has also published an applet for this, but for some reason it fails for me. Also, if you have multiple Google Calendars you use, you can only use one of them with IFTTT. But, pro-tip, you can make multiple IFTTT accounts, one of each calendar.
Explore more great ways to automate Todoist and Google Calendar