You must define the relevant variable to show where your settings.py file lives:
export DJANGO_SETTINGS_MODULE=mysite.settings
This is the relevant docs entry:
When you use Django, you have to tell it which settings you’re using.
Do this by using an environment variable, DJANGO_SETTINGS_MODULE.The value of DJANGO_SETTINGS_MODULE should be in Python path syntax,
e.g. mysite.settings. Note that the settings module should be on the
Python import search path.
If you are using a virtualenv (which is the best practice), you can paste the relevant export command in the file <path-to-virtualenv>/bin/activate