[2.8] Add "How to Use Multiple Guard Authenticators" cookbook documentation#5886

marek-pietrzak-tg wants to merge 6 commits intosymfony:2.8symfony/symfony-docs:2.8from

marek-pietrzak-tg:use_different_entry_pointsmarek-pietrzak-tg/symfony-docs:use_different_entry_pointsCopy head branch name to clipboard