Merge pull request #468 from chenrui333/doc/add-homebrew-install

doc: add homebrew install instruction

Author: calvinli

README.md

@@ -1,5 +1,6 @@
 [![Build Status](https://github.com/Yelp/detect-secrets/actions/workflows/ci.yml/badge.svg)](https://github.com/Yelp/detect-secrets/actions/workflows/ci.yml?query=branch%3Amaster++)
 [![PyPI version](https://badge.fury.io/py/detect-secrets.svg)](https://badge.fury.io/py/detect-secrets)
+[![Homebrew](https://img.shields.io/badge/dynamic/json.svg?url=https://formulae.brew.sh/api/formula/detect-secrets.json&query=$.versions.stable&label=homebrew)](https://formulae.brew.sh/formula/detect-secrets)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-ff69b4.svg)](https://github.com/Yelp/detect-secrets/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22+)
 [![AMF](https://img.shields.io/badge/Donate-Charity-orange.svg)](https://www.againstmalaria.com/donation.aspx)
 
@@ -202,6 +203,12 @@ $ pip install detect-secrets
 ✨🍰✨
 ```
 
+Install via [brew](https://brew.sh/):
+
+```bash
+$ brew install detect-secrets
+```
+
 ## Usage
 
 `detect-secrets` comes with three different tools, and there is often confusion around which one