Add README for building using Vagrant and Ansible

tools/vagrants/README.md

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+# Building in VirtualBox using Vagrant and Ansible
+
+If you want to quickly get Pyston up-and-running in a virtual machine,
+you can use Vagrant to create a virtual machine in VirtualBox
+running Ubuntu 14.04 (Trusty Tahr). The following steps
+use Ansible to run the commands to download and compile Pyston
+plus its dependencies.
+
+
+## Requirements
+
+You need to install:
+
+- [Oracle VirtualBox](https://www.virtualbox.org/wiki/Downloads)
+- [Vagrant](http://downloads.vagrantup.com/)
+- [Ansible](http://docs.ansible.com/intro_installation.html#installing-the-control-machine) - If you're on a Mac and you use [homebrew](http://brew.sh), you can just run "brew install ansible"
+
+## Building
+
+From a checkout directory of Pyston, enter
+the `tools/vagrant` directory, and enter:
+
+```
+$ vagrant up
+```
+
+And then wait a while, probably an hour or two.
+
+## Using the Virtual Machine
+
+Once the machine has finished installing (vagrant calls this provisioning),
+you can connect to it with:
+
+```
+$ vagrant ssh
+```
+
+Then once you're in the virtual machine:
+
+```
+$ cd pyston/src
+$ ./pyston_dbg
+```
+
+
+