MRG: add pyopensci review badge (#3105)

Add pyopensci review badge, linking to accepted review:
pyOpenSci/software-submission#129

README.md

@@ -6,7 +6,9 @@ Quickly search, compare, and analyze genomic and metagenomic data sets.
 <a href="https://github.com/sourmash-bio/sourmash/blob/latest/LICENSE"><img alt="License: 3-Clause BSD" src="https://img.shields.io/badge/License-BSD%203--Clause-blue.svg"></a>
 [![Documentation](https://readthedocs.org/projects/sourmash/badge/?version=latest)](http://sourmash.readthedocs.io/en/latest/)
 [![Gitter](https://badges.gitter.im/sourmash-bio/community.svg)](https://gitter.im/sourmash-bio/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+
 [![DOI](http://joss.theoj.org/papers/10.21105/joss.00027/status.svg)](http://joss.theoj.org/papers/10.21105/joss.00027)
+[![pyOpenSci](https://tinyurl.com/y22nb8up)](https://github.com/pyOpenSci/software-submission/issues/129)
 
 [![Bioconda install](https://img.shields.io/conda/dn/bioconda/sourmash.svg?style=flag&label=Bioconda)](https://anaconda.org/bioconda/sourmash)
 <a href="https://pypi.org/project/sourmash/"><img alt="PyPI" src="https://badge.fury.io/py/sourmash.svg"></a>