docs: add brew install instructions (#951)

website/content/docs/api-clients/desktop.mdx

@@ -26,7 +26,7 @@ $ boundary dev
 
 ### Install Boundary Desktop
 
-1. Download the latest .dmg installer from our [releases page](https://releases.hashicorp.com/boundary-desktop)
+1. Download the latest .dmg installer from our [releases page](https://releases.hashicorp.com/boundary-desktop). Alternatively, if you're a homebrew user, you can run `brew install hashicorp-boundary-desktop`
 1. Double-click the downloaded .dmg to run the installer
 1. Drag and drop Boundary into the applications folder
    ![](/img/boundary-desktop-drag-to-install.png)