Revert "[docs] remove macOS installation method with Homebrew formula (…

…#4122)"

This reverts commit e98da99.

docs/Installation-Guide.rst

@@ -117,13 +117,23 @@ Also, you may want to read `gcc Tips <./gcc-Tips.rst>`__.
 macOS
 ~~~~~
 
-On macOS LightGBM can be built using **CMake** and **Apple Clang** or **gcc**.
+On macOS LightGBM can be installed using **Homebrew**, or can be built using **CMake** and **Apple Clang** or **gcc**.
 
 Apple Clang
 ^^^^^^^^^^^
 
 Only **Apple Clang** version 8.1 or higher is supported.
 
+Install Using ``Homebrew``
+**************************
+
+.. code::
+
+  brew install lightgbm
+
+Build from GitHub
+*****************
+
 1. Install `CMake`_ (3.16 or higher):
 
    .. code::