implement swagger API docs.

[rrmerugu]

This is not a very big change, or task in the code, we just need make some changes in the settings.py and it will automatically do the job.

NOTE: make sure swagger documentation is available only in the dev/local settings or when DEBUG=True

https://django-rest-swagger.readthedocs.io/en/latest/

[pbteja1998]

implemented in #19