Sure.
1) Go to your project folder (%AppData%/Superpowers/projects/ on Windows, see this page)
2) Add your existing git repository as a remote, commit and push
git init
git remote add origin <repourl>
git add .
git commit -m 'Initial commit'
git push -u origin master
This page has some information on superpowers and source control integration.
If you use Windows, you're probably going to need Git for Windows or the Github app. If you're new to git, github has some nice tutorials.