Add documentation for how to develop with the example project

[Ben Alman]

This should be added to the main project README, probably at the bottom.

This assumes that the general workflow dependencies (Ansible, VirtualBox, Vagrant) as well as this project's specific dependencies (Node.js, npm) have been installed.

There are 2 ways to develop the example project.

Using vagrant:

1. vagrant up
2. npm install
3. npm install -g grunt
4. grunt
5. Check the main page: http://deployment-workflow.loc/
6. Check the 404 page: http://deployment-workflow.loc/whoops
7. Edit files locally, pages should auto-reload
8. Repeat steps 5-7

And not using vagrant (this is typically much faster):

1. npm install
2. npm install -g grunt
3. grunt
4. Check the main page: open public/index.html
5. Check the 404 page: open public/404.html
6. Edit files locally, pages should auto-reload
7. Repeat steps 4-6