Add your team name, a link to your demo video, and a link to your main project repository (whatever it is named). To do this, just make it look like the example on line 11.
To save it, Make sure to click the green button at the bottom that says "Propose changes" and then, on the page that follows, create a pull request by clicking the green button that says "Create pull request." See illustration below.
Scroll to the bottom of this page in edit mode and you should see:
Once you have pressed the "Propose changes" button, you should be redirected to this page where you must click the button that says "Create pull request."
