Add JOSS paper badge to README.md (leading)

Author: yarikoptic

README.rst

@@ -4,6 +4,10 @@
 
 `a heuristic-centric DICOM converter`
 
+.. image:: https://joss.theoj.org/papers/10.21105/joss.05839/status.svg
+   :target: https://doi.org/10.21105/joss.05839
+   :alt: JOSS Paper
+
 .. image:: https://img.shields.io/badge/docker-nipy/heudiconv:latest-brightgreen.svg?logo=docker&style=flat
   :target: https://hub.docker.com/r/nipy/heudiconv/tags/
   :alt: Our Docker image