A little confusing that you shows add with new files in the previous lesson, so the M status in the first example isn't something that the students will have come across. I'd suggest either adding a further modification to the last example, or explaining in this lesson that it means that hte content has been modified.
Also: "If you leave out the -m flag and the message that follows it ..."
One final note: these coments take an AGE to process. I hope this is because the site is busy ... because if not it will never get busy - it will be too slow!