add readme badges for CI status, min supported py version, current PyPI release and monthly downloads

Author: janosh

.github/workflows/test.yml

@@ -1,4 +1,4 @@
-name: Testing
+name: Tests
 
 on:
   push:

README.md

@@ -1,5 +1,10 @@
 # <img alt="atomate" src="docs_rst/_static/atomate_logo_small.png" width="250">
 
+[![Tests](https://github.com/hackingmaterials/atomate/actions/workflows/test.yml/badge.svg)](https://github.com/hackingmaterials/atomate/actions/workflows/test.yml)
+[![PyPI Downloads](https://img.shields.io/pypi/dm/atomate?label=PyPI%20Downloads)](https://pypi.org/project/atomate)
+[![PyPI](https://img.shields.io/pypi/v/atomate?label=PyPI%20Release)](https://pypi.org/project/atomate)
+[![Requires Python 3.8+](https://img.shields.io/badge/Python-3.8+-blue.svg?label=Requires%20Python)](https://python.org/downloads)
+
 atomate is a software for computational materials science that contains pre-built workflows to compute and analyze the properties of materials.
 
 - **Website (including documentation):** https://hackingmaterials.github.io/atomate/