Add a newbie guide for people completely new to QMK (#2480)

util/macos_install.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+if brew --version 2>&1 > /dev/null; then
+	echo "Error! Homebrew not installed or broken!"
+	echo -n "Would you like to install homebrew now? [y/n] "
+	while read ANSWER; do
+		case $ANSWER in
+			y|Y)
+				/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
+				break
+			;;
+			n|N)
+				exit 1
+			;;
+			*)
+				echo -n "Would you like to install homebrew now? [y/n] "
+			;;
+                esac
+	done
+fi
+
+brew tap osx-cross/avr
+brew tap PX4/homebrew-px4
+brew update
+brew install avr-gcc gcc-arm-none-eabi dfu-programmer avrdude