So we could make it so there is two senarios:
 1. Github user has a public email on github and we can fetch it using github API.
     (ie. we don't take the email from git commit message, so we know the email belongs to github user)
 2. If github user doesn't have a public email, we use some sort of pseudo email. Say `<github-username>@github.taskcluster.net`.

People who register a public email with github will be able to modify tasks/task-graphs when logged in with persona. People who don't give a public email address on github, will not have a way to login (in far future we could validate with github API, but this is probably overkill).

This scheme would allow us to identify users, and not require a public email. You just get a slightly degraded experience if you don't have a public email. I'm guessing most people won't use persona login for anything anyway, so it doesn't matter.

**Note**, please add github username as a tag. This might be useful when we make a UI to search for submitted tasks and task-graphs.