fix: reformat the zenodo badge in the readme

Author: pgierz

README.rst

@@ -15,7 +15,8 @@
 .. image:: https://img.shields.io/github/license/esm-tools/pymor
     :target: https://pymor.readthedocs.io/en/latest/?badge=latest
 .. image:: https://zenodo.org/badge/DOI/10.5281/zenodo.15530131.svg
-  :target: https://doi.org/10.5281/zenodo.15530131
+    :target: https://doi.org/10.5281/zenodo.15530131
+
 ------