Add Homebrew instructions to readme

Author: christianbundy

README.md

@@ -29,6 +29,7 @@ Alternatively, you can install Patchwork with your favorite package manager.
 
 - **[npm][npm]:** `npm install --global ssb-patchwork`
 - **[yarn][yarn]:** `yarn global add ssb-patchwork`
+- **[brew][brew]:** `brew cask install patchwork`
 - **[yay][yay]:** `yay -S ssb-patchwork`
 
 Building from source? Check out [`INSTALL.md`][install] for more information.
@@ -52,6 +53,7 @@ terms.
 
 [AGPL-3.0][license]
 
+[brew]: https://brew.sh
 [conduct]: docs/CODE_OF_CONDUCT.md
 [contributing]: docs/CONTRIBUTING.md
 [gh-dl]: https://github.com/ssbc/patchwork/releases/latest