Updated Working on macOS (markdown)

Working-on-macOS.md

@@ -60,9 +60,24 @@ Building statically means you can run this application on other machines with ea
 
 ## Here's the quick instructions:
 
-1. From the command line:
-`export MACOSX_DEPLOYMENT_TARGET=10.9`
-2. Build raylib (Again, this is so the export line takes affect) 
+1. From the command line: `export MACOSX_DEPLOYMENT_TARGET=10.9`
+2. Install prerequisite external libraries (GLFW, GLUT, etc.) In terminal:
+* Install XCode tools (don't forget to then update the tools in the Mac App Store after!)
+````
+xcode-select --install
+````
+
+* Install Homebrew:
+````
+/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
+````
+
+* Install GLFW
+````
+brew install glfw
+````
+
+3. Build raylib (Again, this is so the export line takes effect) 
 
 ````
 git clone https://github.com/raysan5/raylib.git