[docs] added installation guide with Homebrew (#2414)

* added installation guide with Homebrew

* hotfix

* update wording to separate install and build cases

docs/Installation-Guide.rst

@@ -111,13 +111,23 @@ 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`_ (3.12 or higher):
 
    .. code::