Added postgres notes

[lpatmo]

See: #12

[BethanyG]

With the new settings file using django-environ, django will expect an env variable (either in the environment or in a .env file) called DATABASE_URL. It should take the form of this:

postgres://{user}:{password}@{hostname}:{port}/{database-name}

as an example:
postgres://silly_username:a_password@localhost:5342/your_db_name_here

env.db() will then parse this into a DATABASE dict automatically for Djangos use in settings.

[brylie]

If there are no other improvements, let's go ahead and merge this PR :-)

[lpatmo]

Oof... I know these instructions I wrote up quickly aren't the best and @bengineerdavis wanted to work on something clearer, but they are better than the status quo at the moment. So will merge so it's in history, and we can update these in a future PR.