chore: update readme

Author: dancixx

README.md

@@ -1,6 +1,7 @@
 ![Build Workflow](https://github.com/dancixx/stochastic-rs/actions/workflows/rust.yml/badge.svg)
 [![Crates.io](https://img.shields.io/crates/v/stochastic-rs?style=flat-square)](https://crates.io/crates/stochastic-rs)
 ![License](https://img.shields.io/crates/l/stochastic-rs?style=flat-square)
+[![codecov](https://codecov.io/gh/dancixx/stochastic-rs/graph/badge.svg?token=SCSp3z7BQJ)](https://codecov.io/gh/dancixx/stochastic-rs)
 [![FOSSA Status](https://app.fossa.com/api/projects/git%2Bgithub.com%2Fdancixx%2Fstochastic-rs.svg?type=shield)](https://app.fossa.com/projects/git%2Bgithub.com%2Fdancixx%2Fstochastic-rs?ref=badge_shield)
 
 # stochastic-rs