added codecov badge to README

README.md

@@ -1,4 +1,5 @@
 [![CI](https://github.com/poseidon-framework/poseidon-analysis-hs/actions/workflows/main.yml/badge.svg)](https://github.com/poseidon-framework/poseidon-analysis-hs/actions/workflows/main.yml)
+[![Coverage Status](https://img.shields.io/codecov/c/github/poseidon-framework/poseidon-analysis-hs/main.svg)](https://codecov.io/github/poseidon-framework/poseidon-analysis-hs?branch=main)
 [![GitHub release (latest by date including pre-releases)](https://img.shields.io/github/v/release/poseidon-framework/poseidon-analysis-hs?include_prereleases) ![GitHub all releases](https://img.shields.io/github/downloads/poseidon-framework/poseidon-analysis-hs/total)](https://github.com/poseidon-framework/poseidon-analysis-hs/releases)
 [![Install with Bioconda](https://anaconda.org/bioconda/poseidon-xerxes/badges/version.svg)](https://anaconda.org/bioconda/poseidon-xerxes)
 [![Anaconda-Server Badge](https://anaconda.org/bioconda/poseidon-xerxes/badges/downloads.svg)](https://anaconda.org/bioconda/poseidon-xerxes)