Add an entry in the Alert menu to explain what it's for

Right now users won't know easily what the Alert menu is for. It would be nice and helpful that we add an entry in this menu (with the ability for Admin users to remove it by clicking some X or "Dismiss" button) and that will explain what users should be able to see in this menu and how to use it.

It would also add the red count to 1 when you log in initially, drawing attention to the alert menu so that users can discover it.

Something similar to: