start of docker docs

Not sure about this. Currently wharfie's checkout is assuming you'd set whoami to *your* username as it is going to checkout *your* forks and then it adds mozilla as an 'upstream' remote as part of the checkout command.

Maybe we can do it this way but we should think about changing wharfie's default behaviour. Also we should think about what remotes are set to and have a sane default. 

For example I use **origin** for my remote and **upstream** for the mozilla upstream. This approach matches github's docs. https://help.github.com/articles/fork-a-repo so it's a good default.

So for these instructions to be good wharfie's command should be updated to use `git clone --origin upstream [mozilla repo]`