Add howfairis badge. (#308)

Author: dcherian

README.rst

@@ -29,6 +29,9 @@
 .. image:: https://zenodo.org/badge/267381269.svg
    :target: https://zenodo.org/badge/latestdoi/267381269
 
+.. image:: https://img.shields.io/badge/fair--software.eu-%E2%97%8F%20%20%E2%97%8F%20%20%E2%97%8F%20%20%E2%97%8F%20%20%E2%97%8B-yellow
+   :target: https://fair-software.eu
+
 cf-xarray
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