add readme file
add readme file

gencer/oauth2-php,aaasayok/oauth2-php,soleo/oauth2-php,nnmer/oauth2-php,quizlet/oauth2-php-closed-source,box/oauth2-php,borNfreee/oauth2-php,FriendsOfSymfony/oauth2-php,danielfleck/oauth2-php,SergioEnrique/oauth2-php,McOffsky/oauth2-php