Setting this option (which we do [here](https://github.com/hypothesis/h/blob/f3ea4b521fc30cba2e201592eb357f3d97f43660/h/templates/annotation.html#L64)) hides the "markdown is supported" tip, [here](https://github.com/hypothesis/h/blob/f3ea4b521fc30cba2e201592eb357f3d97f43660/h/templates/markdown.html#L3).