Notifications has many of my favorite Apps in it, however, Time Machine is conspicuously absent.

I read [here](http://www.apple.com/osx/whats-new/features.html) that it should be showing:

> 
> System notifications System alerts with updates about your battery,
>  Time Machine backups, and ejected disks appear as notifications, so
>  you can easily spot them with the rest of your notifications.
> 
> 
> 

How do I add Time Machine to the list?