Adding JOSS article to readme

Author: michaeldenes

README.md

@@ -1,7 +1,7 @@
 ## plasticparcels
 `plasticparcels` is a python package for simulating the transport and dispersion of plastics in the ocean.
 
-The tool is based on the [`Parcels`](https://oceanparcels.org/) computational Lagrangian ocean analysis framework ([@Lange2017](http://dx.doi.org/10.5194/gmd-10-4175-2017) and [@Delandmeter2019](http://dx.doi.org/10.5194/gmd-12-3571-2019)), providing a modular and customisable collection of methods, notebooks, and tutorials for advecting virtual plastic particles with a wide range of physical properties.
+The tool is based on the [`Parcels`](https://oceanparcels.org/) computational Lagrangian ocean analysis framework ([@Lange2017](http://dx.doi.org/10.5194/gmd-10-4175-2017) and [@Delandmeter2019](http://dx.doi.org/10.5194/gmd-12-3571-2019)), providing a modular and customisable collection of methods, notebooks, and tutorials for advecting virtual plastic particles with a wide range of physical properties. A peer reviewed paper describing `plasticparcels` can be found here: [![DOI](https://joss.theoj.org/papers/10.21105/joss.07094/status.svg)](https://doi.org/10.21105/joss.07094).
 
 ![plasticparcels](docs/_static/plasticparcelslogo.png)
 
@@ -44,6 +44,7 @@ If you would like support using `plasticparcels`, or are have any questions abou
 ### Further information
 For more information and documentation, see the [plasticparcels documentation](https://plastic.oceanparcels.org/).
 
+[![DOI](https://joss.theoj.org/papers/10.21105/joss.07094/status.svg)](https://doi.org/10.21105/joss.07094)
 [![unit-tests](https://github.com/OceanParcels/plasticparcels/actions/workflows/unit_tests.yml/badge.svg)](https://github.com/OceanParcels/plasticparcels/actions/workflows/unit_tests.yml)
 [![Anaconda-release](https://anaconda.org/conda-forge/plasticparcels/badges/version.svg)](https://anaconda.org/conda-forge/plasticparcels/)
 [![Anaconda-date](https://anaconda.org/conda-forge/plasticparcels/badges/latest_release_date.svg)](https://anaconda.org/conda-forge/plasticparcels/)