Update README.md

Author: thomasrockhu-codecov

README.md

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 # [Codecov](https://codecov.io) Python Example
-[![codecov](https://codecov.io/github/codecov/example-python/branch/master/graph/badge.svg?token=tkq655ROg3)](https://app.codecov.io/github/codecov/example-python)
+[![codecov](https://codecov.io/github/codecov/example-python/branch/main/graph/badge.svg?token=tkq655ROg3)](https://app.codecov.io/github/codecov/example-python)
 [![FOSSA Status](https://app.fossa.com/api/projects/git%2Bgithub.com%2Fcodecov%2Fexample-python.svg?type=shield)](https://app.fossa.com/projects/git%2Bgithub.com%2Fcodecov%2Fexample-python?ref=badge_shield)
 
 This example repository shows how Codecov can be integrated with a simple python project. It uses **GitHub Actions** and **CircleCI** as CI/CD providers and **coverage** as the coverage provider.