Add missing pypi stat link

Author: XkunW

README.md

@@ -3,7 +3,7 @@
 ----------------------------------------------------
 
 [![PyPI](https://img.shields.io/pypi/v/vec-inf)](https://pypi.org/project/vec-inf)
-[![downloads](https://img.shields.io/pypi/dm/vec-inf)]
+[![downloads](https://img.shields.io/pypi/dm/vec-inf)](https://pypistats.org/packages/vec-inf)
 [![code checks](https://github.com/VectorInstitute/vector-inference/actions/workflows/code_checks.yml/badge.svg)](https://github.com/VectorInstitute/vector-inference/actions/workflows/code_checks.yml)
 [![docs](https://github.com/VectorInstitute/vector-inference/actions/workflows/docs.yml/badge.svg)](https://github.com/VectorInstitute/vector-inference/actions/workflows/docs.yml)
 [![codecov](https://codecov.io/github/VectorInstitute/vector-inference/branch/main/graph/badge.svg?token=NI88QSIGAC)](https://app.codecov.io/github/VectorInstitute/vector-inference/tree/main)