add recommended brew method to install emacs

README.md

@@ -171,6 +171,18 @@ After completing the Spacemacs [install process](#install), then it's also
 recommended to add the [osx layer][] to your [dotfile][]. Installation
 instructions are available in the documentation for the [osx layer][].
 
+#### Recommended by Brew
+
+Brew now recommends emacs to be installed as:
+
+```
+brew cask install emacs
+```
+
+But that doesn't create `/usr/local/bin/emacs`.
+
+You may follow [Emacs for Mac OS X, Tips](https://emacsformacosx.com/tips) on how to create scripts for running emacs and emacsclient.
+
 ### Windows
 You can download good quality builds from the [emacs-w64 project][emacs-for-windows].
 It is recommended to install the most recent [stable build][emacs-for-windows-stable].