feat(dotenv): add django-dotenv support.

manage.py do not read `.env`. Let's fix that.

Usecase:
While working b/w different project it's becomes
difficult to work with environment variables.
Also we don't want to track the local enviroment
varibale.

Solution:
Using django-dotenv[1], we can save all the local
environment per project in a .env file. This file
should not be tracked, instead a .env.sample should
be used to educated the user for possible environment
variables.

[1] https://github.com/jacobian/django-dotenv