Add guide to security README [ci skip].

Author: geerlingguy

security/README.md

@@ -2,9 +2,23 @@
 
 This directory contains playbooks used for security hardening with Ansible, and is meant as a companion to the examples and text in chapter 11 of [Ansible for DevOps](https://www.ansiblefordevops.com).
 
-## Usage
+## Quick Start Guide
 
-TODO.
+### 1 - Install dependencies (VirtualBox, Vagrant, Ansible)
+
+  1. Download and install [VirtualBox](https://www.virtualbox.org/wiki/Downloads).
+  2. Download and install [Vagrant](http://www.vagrantup.com/downloads.html).
+  3. [Mac/Linux only] Install [Ansible](http://docs.ansible.com/intro_installation.html).
+
+Note for Windows users: *This guide assumes you're on a Mac or Linux host. Windows hosts are unsupported at this time.*
+
+### 2 - Build the Virtual Machine
+
+  1. Download this project and put it wherever you want.
+  2. Open Terminal, cd to this directory (containing the `Vagrantfile` and this README file).
+  3. Type in `vagrant up`, and let Vagrant do its magic.
+
+Note: *If there are any errors during the course of running `vagrant up`, and it drops you back to your command prompt, just run `vagrant provision` to continue building the VM from where you left off. If there are still errors after doing this a few times, post an issue to this project's issue queue on GitHub with the error.*
 
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