Custom button names must be lower-case

Custom button names must be lower-case, and can not have an initial capital letter, otherwise they do not appear. It might be worth (a) noting this in the instructions (in additional to mentioning no special characters) (b) Perform a check.

Since it took me a while to find it, on the Settings page in the Toolbar section, how about adding the text "To make custom buttons click the Custom Buttons tab top-right".