Add download badge to README (#7)

Author: AnshMNSoni

README.md

@@ -1,5 +1,6 @@
 # PythonSTL - Python Standard Template Library
 
+[![Downloads](https://img.shields.io/pypi/dw/pythonstl.svg)](https://pypi.org/project/pythonstl/)
 [![Python Version](https://img.shields.io/badge/python-3.10%2B-blue.svg)](https://www.python.org/downloads/)
 [![PyPI version](https://img.shields.io/pypi/v/pythonstl.svg)](https://pypi.org/project/pythonstl/)
 [![License](https://img.shields.io/badge/license-MIT-green.svg)](LICENSE)