Add Zenodo badge (#14)

Author: devmotion

README.md

@@ -6,6 +6,7 @@
 [![Dev](https://img.shields.io/badge/docs-dev-blue.svg)](https://juliaoptimaltransport.github.io/PythonOT.jl/dev)
 [![Build Status](https://github.com/JuliaOptimalTransport/PythonOT.jl/workflows/CI/badge.svg?branch=main)](https://github.com/JuliaOptimalTransport/PythonOT.jl/actions?query=workflow%3ACI+branch%3Amain)
 [![Build Status (Julia nightly)](https://github.com/JuliaOptimalTransport/PythonOT.jl/workflows/JuliaNightly/badge.svg?branch=main)](https://github.com/JuliaOptimalTransport/PythonOT.jl/actions?query=workflow%3AJuliaNightly+branch%3Amain)
+[![DOI](https://zenodo.org/badge/364887971.svg)](https://zenodo.org/badge/latestdoi/364887971)
 [![Coverage](https://codecov.io/gh/JuliaOptimalTransport/PythonOT.jl/branch/main/graph/badge.svg)](https://codecov.io/gh/JuliaOptimalTransport/PythonOT.jl)
 [![Coverage](https://coveralls.io/repos/github/JuliaOptimalTransport/PythonOT.jl/badge.svg?branch=main)](https://coveralls.io/github/JuliaOptimalTransport/PythonOT.jl?branch=main)
 [![Code Style: Blue](https://img.shields.io/badge/code%20style-blue-4495d1.svg)](https://github.com/invenia/BlueStyle)