Update README.rst badge to restructured text

Author: yoachim

README.rst

@@ -3,8 +3,8 @@
 .. image:: https://github.com/lsst-sims/smtn-018/workflows/CI/badge.svg
    :target: https://github.com/lsst-sims/smtn-018/actions/
 
-
-[![DOI](https://zenodo.org/badge/635502244.svg)](https://doi.org/10.5281/zenodo.14783622)
+.. image:: https://zenodo.org/badge/635502244.svg
+  :target: https://doi.org/10.5281/zenodo.14783622
 
 
 #############################