title: I added a SECRET_KEY config variable to my Django app on Heroku but now it won't work locally
body: <p>I changed my secret key to an environment variable on my Heroku app. I changed it because I found out that keeping the secret key in <code>settings.py</code> was a security risk.</p>
  
  <p>However, now it won't work locally when I use <code>python manage.py runserver</code>. It gives an error about the secret key.</p>
  
  <p>How do I fix it so I can develop my Heroku app locally?</p>