Update README.rst

README.rst

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  GalMag - A Python tool for computing realistic galactic magnetic fields
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-|doi| |rtd|
+|doi| |rtd| |arxiv|
 
 `GalMag <https://github.com/luizfelippesr/galmag>`_ is a
 `Python <http://www.python.org>`_  package for computing galactic magnetic
@@ -67,8 +67,7 @@ References
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 .. [1] Shukurov et al., "A physical model of the galactic large-scale magnetic field",
-    MNRAS, submitted
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+    MNRAS (submitted), `arXiv:1809.03595 <https://arxiv.org/abs/1809.03595/>`_.
 
 .. |doi| image:: https://zenodo.org/badge/DOI/10.5281/zenodo.1135246.svg
    :target: https://doi.org/10.5281/zenodo.1135246
@@ -77,3 +76,7 @@ References
 .. |rtd| image:: https://readthedocs.org/projects/galmag/badge/?version=latest
    :target: http://galmag.readthedocs.io/en/latest/?badge=latest
    :alt: Documentation Status
+
+.. |arxiv| image:: http://img.shields.io/badge/arXiv-1809.03595-B31B1B.svg
+   :target: https://arxiv.org/abs/1809.03595
+   :alt: Code Paper ArXiv ID