Update README.md to reflect JOSS paper

README.md

@@ -7,7 +7,7 @@
 ╚═╝        ╚═╝   ╚═╝  ╚═╝ ╚═════╝ ╚═╝  ╚═╝╚══════╝
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-![example workflow](https://github.com/sisl/PyroRL/actions/workflows/testing.yml/badge.svg) [![codecov](https://codecov.io/github/sisl/PyroRL/graph/badge.svg?token=wBlFGsd5sS)](https://codecov.io/github/sisl/PyroRL) [![](https://img.shields.io/badge/docs-latest-blue.svg)](https://sisl.github.io/PyroRL/)
+![example workflow](https://github.com/sisl/PyroRL/actions/workflows/testing.yml/badge.svg) [![codecov](https://codecov.io/github/sisl/PyroRL/graph/badge.svg?token=wBlFGsd5sS)](https://codecov.io/github/sisl/PyroRL) [![](https://img.shields.io/badge/docs-latest-blue.svg)](https://sisl.github.io/PyroRL/)  [![DOI](https://joss.theoj.org/papers/10.21105/joss.06739/status.svg)](https://doi.org/10.21105/joss.06739)
 
 PyroRL is a new reinforcement learning environment built for the simulation of wildfire evacuation. Check out the [docs](https://sisl.github.io/PyroRL/) and the [demo](https://www.loom.com/share/39ddd19c790a49c0a1ea7e13cd4d1005?sid=679b631a-74b7-41e3-bd88-3e7d14c0adc2).