Added note in FAQ as per https://github.com/jupyter/nbgrader/issues/822
Added note in FAQ as per https://github.com/jupyter/nbgrader/issues/822

jupyter/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,jhamrick/nbgrader,jhamrick/nbgrader