draft init requires email, although it's not really needed by the OSS registry

[SteveLasker]

When following: https://github.com/Azure/draft/blob/master/docs/install.md I see the command

$ echo '{"username":"jdoe","password":"secret","email":"[email protected]"}' | base64

Knowing registries don't actually require email, I just took it off. After a 'draft up' I got the error:
Error encountered streaming JSON response: no basic auth credentials
It took a while to even get this far, as CLIs don't apparently do auto-correct :(. So, it took a bit more to make sure the username/password combination were proper and just happen to try adding the email.
Based on the refactor, I see this encoding may go away, which would be perfect. But, I would imagine there'd be a CLI that still took --username --password, and just suggesting we remove any dependency for the user to pass in email.
Was going to do a PR for the docs to note this requirement until the refactoring is done, but I believe the change is quickly pending.

[bacongobbler]

This is actually going completely away in #154. We only ask for the user's username and password moving forward.