Update 2-integration-with-fosuserbundle.md

Annotations so certain IDEs will not complain about unknown methods (PHPStorm for me) and added a $userProvider which is suggested by the UserManager class because userManager->supportsClass() is deprecated on the userManager and suggests to use UserProvider.

I changed the annotation of $facebook based on the argument in config.yml it points to the fos_facebook.api service which is the class I put above.