Update settings.rst
Update settings.rst

For the django strategy at least, the AUTH_EXTRA_ARGUMENTS settings still need to be prefixed with SOCIAL_AUTH_ to be recognized.
python-social-auth/social-storage-sqlalchemy,cjltsod/python-social-auth,contracode/python-social-auth,rsalmaso/python-social-auth,S01780/python-social-auth,S01780/python-social-auth,contracode/python-social-auth,webjunkie/python-social-auth,python-social-auth/social-app-django,tobias47n9e/social-core,merutak/python-social-auth,tkajtoch/python-social-auth,python-social-auth/social-app-django,falcon1kr/python-social-auth,python-social-auth/social-docs,fearlessspider/python-social-auth,tkajtoch/python-social-auth,fearlessspider/python-social-auth,merutak/python-social-auth,python-social-auth/social-app-cherrypy,rsalmaso/python-social-auth,contracode/python-social-auth,webjunkie/python-social-auth,falcon1kr/python-social-auth,python-social-auth/social-core,merutak/python-social-auth,cjltsod/python-social-auth,S01780/python-social-auth,python-social-auth/social-core,fearlessspider/python-social-auth,python-social-auth/social-app-django,tkajtoch/python-social-auth,falcon1kr/python-social-auth,webjunkie/python-social-auth