Add version control (Git)

[danieldraper]

Thoughts on adding basic Git usage to the guide?

• git global config before git usage
• git init followed by an initial commit after rails new
• git add and git commit after adding posts
• git add and git commit after adding authentication
• git add and git commit after adding comments

This will introduce a very basic git workflow in preparation for deploying to Heroku while also familiarising participants with the very basics of best practice.