Update public/postreceive.php - safer and more accurate updating.

This ensures the response is from github using our personal secret key.
postreceive.php: Now fully functional and secure.
Update README.md
Merge branch 'master' of github.com:Zarthus/potential-happiness
Merge branch 'master' of github.com:Zarthus/potential-happiness
Merge branch 'master' of github.com:Zarthus/potential-happiness