Update docs/settings.rst
Update docs/settings.rst

Documented GOOGLE_APPLICATION_CREDENTIALS env var

Co-Authored-By: vladdoster <9528de133d673d7b6619c01048d663b9f747c9ad@wit.edu>
Parbhat/cookiecutter-django-foundation,luzfcb/cookiecutter-django,ad-m/cookiecutter-django,trungdong/cookiecutter-django,trungdong/cookiecutter-django,ad-m/cookiecutter-django,ryankanno/cookiecutter-django,ryankanno/cookiecutter-django,pydanny/cookiecutter-django,ad-m/cookiecutter-django,Parbhat/cookiecutter-django-foundation,luzfcb/cookiecutter-django,luzfcb/cookiecutter-django,Parbhat/cookiecutter-django-foundation,trungdong/cookiecutter-django,pydanny/cookiecutter-django,ryankanno/cookiecutter-django,Parbhat/cookiecutter-django-foundation,trungdong/cookiecutter-django,ad-m/cookiecutter-django,pydanny/cookiecutter-django,pydanny/cookiecutter-django,luzfcb/cookiecutter-django,ryankanno/cookiecutter-django