add more badges

Author: soldatov-ss

README.md

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 # django-referral-system
 
 ![Documentation Status](https://readthedocs.org/projects/django-referral-system/badge/?version=latest)
+[![PyPI version](https://badge.fury.io/py/django-referral-system.svg)](https://badge.fury.io/py/django-referral-system)
+[![License](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/soldatov-ss/django-referral-system/blob/main/LICENSE)
+[![Python Versions](https://img.shields.io/pypi/pyversions/django-referral-system.svg)](https://pypi.org/project/django-referral-system/)
 
 A Django app for managing referral programs, promoters, referrals, and tracking referral performance with features like
 commission setting, invitation management, and Wise payouts.