docs: add pypi downloads stats badge #114

Job	Run time
Linting	3m 9s
Pytest (3.7)	2m 1s
Installation (3.7)	1m 19s
Pytest (3.8)	2m 1s
Installation (3.8)	4m 29s
Pytest (3.9)	1m 46s
Installation (3.9)	1m 36s
Pytest (3.10)	2m 9s
Installation (3.10)	1m 35s
Pytest (3.11)	2m 3s
Installation (3.11)	1m 43s
Coverage / Update Base Coverage	18s
Coverage / Check Pull Request Coverage	0s
	24m 9s

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