Add link URL to site to GitHub summary

[eliotsykes]

After "First Aid Git", it'd be handy to have a URL to http://ricardofilipe.com/projects/firstaidgit/#/ (also near the top of the README would be 👍 )

[hzoo]

👍 or http://firstaidgit.io/

[RichardLitt]

@magalhini Only you can do this. Alternatively, make me an admin. :)