Speaking as a github newbie: It would be nice to emphasize that using `-f` (`--force`) is _safe_ when pushing to a github branch that is part of a PR. This is useful, since all documentation on rebasing I've seen on the web says never to rebase a branch you have shared with others, a rule which for a beginner seems applicable also to a github PR and its corresponding feature branch in the personal fork.

A detail: I'd prefer `--force` over `-f`.