The documentation doesn't really talk about forks. Most people are likely to encounter this as part of attempting to collaborate on their own drafts, so maybe this isn't the first thing to talk about, but we really do want people to contribute to other drafts (that's most of the point of this).
The GitHub flow is not intuitive at first, so you really need to talk about repositories and forks. That is, you maintain a copy of the repository with your own commits, branches, and state. Then you make a branch on that fork with the changes that you want to propose. Pull requests are created from that branch and pull the necessary commits from the source branch into the target repository.
The documentation doesn't really talk about forks. Most people are likely to encounter this as part of attempting to collaborate on their own drafts, so maybe this isn't the first thing to talk about, but we really do want people to contribute to other drafts (that's most of the point of this).
The GitHub flow is not intuitive at first, so you really need to talk about repositories and forks. That is, you maintain a copy of the repository with your own commits, branches, and state. Then you make a branch on that fork with the changes that you want to propose. Pull requests are created from that branch and pull the necessary commits from the source branch into the target repository.