Add bors badge to readme

[ci skip]

README.md

@@ -4,6 +4,7 @@ _formerly pyo3-pack_
 
 [![Actions Status](https://img.shields.io/github/workflow/status/pyo3/maturin/Test?logo=github&style=flat-square)](https://github.com/PyO3/maturin/actions)
 [![FreeBSD](https://img.shields.io/cirrus/github/PyO3/maturin/main?logo=CircleCI&style=flat-square)](https://cirrus-ci.com/github/PyO3/maturin)
+[![Bors enabled](https://bors.tech/images/badge_small.svg)](https://app.bors.tech/repositories/55651)
 [![Crates.io](https://img.shields.io/crates/v/maturin.svg?logo=rust&style=flat-square)](https://crates.io/crates/maturin)
 [![PyPI](https://img.shields.io/pypi/v/maturin.svg?logo=python&style=flat-square)](https://pypi.org/project/maturin)
 [![Maturin User Guide](https://img.shields.io/badge/user-guide-brightgreen?logo=readthedocs&style=flat-square)](https://maturin.rs)