docs: inline updated mac homebrew instructions

The instructions at `http://www.pointclouds.org/documentation/tutorials/installing_homebrew.php` are out of date and no longer working since`brew tap homebrew/science` was deprecated.

README.md

@@ -25,8 +25,17 @@ http://www.pointclouds.org/downloads/windows.html
 
 ### MAC
 
+#### Install via Homebrew
+1. install [homebrew](https://brew.sh/)
+2. update homebrew `$> brew update`
+3. add  homebrew science [tap](https://docs.brew.sh/Taps) `$> brew tap brewsci/science`
+4. view pcl install options `$> brew options pcl`
+5. install PCL `$> brew install pcl`
+
+#### Prebuilt Binaries via Universal Installer
 http://www.pointclouds.org/downloads/macosx.html
-http://www.pointclouds.org/documentation/tutorials/installing_homebrew.php
-
-
+NOTE: very old version 
 
+#### Build from Source
+[PCL Source Github](https://github.com/PointCloudLibrary/pcl)
+[PCL Mac Compilation Docs](http://www.pointclouds.org/documentation/tutorials/compiling_pcl_macosx.php)