update: readme

README.md

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 <img src="docs/assets/ml4co-kit-logo.png" alt="ML4CO-Kit" width="800"/>
 
-[![PyPi version](https://badgen.net/pypi/v/data4co/)](https://pypi.org/pypi/data4co/)[![PyPI pyversions](https://img.shields.io/badge/dynamic/json?color=blue&label=python&query=info.requires_python&url=https%3A%2F%2Fpypi.org%2Fpypi%2Fdata4co%2Fjson)](https://pypi.python.org/pypi/data4co/)[![Downloads](https://static.pepy.tech/badge/data4co)](https://pepy.tech/project/data4co)[![GitHub stars](https://img.shields.io/github/stars/Thinklab-SJTU/ML4CO-Kit.svg?style=social&label=Star&maxAge=8640)](https://GitHub.com/Thinklab-SJTU/ML4CO-Kit/stargazers/) 
+[![PyPi version](https://badgen.net/pypi/v/data4co/)](https://pypi.org/pypi/data4co/) [![PyPI pyversions](https://img.shields.io/badge/dynamic/json?color=blue&label=python&query=info.requires_python&url=https%3A%2F%2Fpypi.org%2Fpypi%2Fdata4co%2Fjson)](https://pypi.python.org/pypi/data4co/) [![Downloads](https://static.pepy.tech/badge/data4co)](https://pepy.tech/project/data4co) [![GitHub stars](https://img.shields.io/github/stars/Thinklab-SJTU/ML4CO-Kit.svg?style=social&label=Star&maxAge=8640)](https://GitHub.com/Thinklab-SJTU/ML4CO-Kit/stargazers/) 
 
 `ML4CO-Kit` is a in-development toolkit for machine learning practices on combinatorial optimization problems, which is a by-product of our research for a unified modular framework that integrates existing ML4CO practices, minimizing disparities among methods and supporting the investigations via in-depth analysis and transparent ablation.