How can I add a vimeo video to each post (project) on hugo-freelancer-theme

For this theme
http://themes.gohugo.io/theme/freelancer/
I want to be able to click an image under ‘portfolio’ and have it show a vimeo video instead of the same image.
Each project.yaml only contains the following

modalID: 1
title: Project Cabin
date: 2014-07-13
img: cabin.png
client: Start Bootstrap
clientLink: "#"
category: Web Development
description: My description