docs/devices: add M345 (HID++ 2.0)

Now I have 5 devices should I have to perform any tests, 2 to go for testing the 6 device limit. What is this "smooth scrolling"? Both the M345 and my M525 have a sensitive scroll wheel, is that meant by "smooth scrolling"?

(these mice also have back/forward buttons, i.e. press the scroll wheel to the left/right for sending a back/forward action)