I wanted to do this as well. I found the best solution for myself was to use the MMM-Wunderlist module.
(You need the Wunderlist app on your mobile device as well. )


It’s a ToDo list and you can get messages to show up on the mirror by adding them to a specific List.
This way you can have multiple messages showing up. And to get rid of the messages you can just tick that item off the list.
You can also share lists with other Wunderlist users so they can also add and tick of items.

One thing I did find as well is that it did stop updating after so many hours of running. Never found out what caused this, there are some other threads on here regarding the same issue (the same with ToDoist module)
The way I got around that was to set up a schedule to restart the MagicMirror a few times a day.

Hope this helps or that you find an alternative solution, would be interested if there was an alternative easier way.