A developer can revert their own commits on their own branches well-enough by using `git revert`.

This is more for Github's "Enterprise-y" (or "distributed FOSS project-y") workflow, where you have

• a project maintainer, who never touches git, and works entirely through Github, interacting mostly with the issue tracker and only modifying the codebase by accepting/rejecting pull-requests; and

• a set of developers, who actually use git, and generate pull-requests to submit to the maintainer.

Until now, if the non-git-using maintainer accepted a pull-request they shouldn't have, they would have to get one of the developers to create a reverting commit, create a PR for that commit, and then accept the PR. Now they can just revert the PR itself.