Added codefactor badge [skip ci]

README.md

@@ -1,3 +1,4 @@
 # Single Sign On for GLPI
 
 [![Build Status](https://travis-ci.org/edgardmessias/glpi-singlesignon.svg?branch=master)](https://travis-ci.org/edgardmessias/glpi-singlesignon)
+[![CodeFactor](https://www.codefactor.io/repository/github/edgardmessias/glpi-singlesignon/badge)](https://www.codefactor.io/repository/github/edgardmessias/glpi-singlesignon)