added doc link for free ssl certificate

Author: Augustinetharakan12

README.md

@@ -36,4 +36,6 @@ python manage.py runserver
 
 [https://www.django-rest-framework.org/](https://www.django-rest-framework.org/)
 
+[https://www.sslforfree.com/](https://www.sslforfree.com/)
+
 [https://simpleisbetterthancomplex.com/tutorial/2016/10/14/how-to-deploy-to-digital-ocean.html](https://simpleisbetterthancomplex.com/tutorial/2016/10/14/how-to-deploy-to-digital-ocean.html)