[Feature request] Add some help when call ace-window

[ghost]

When user call ace-window function, it would be cool to display a little help in the minibuffer.

For example: Select a window [1--3] or an action, type [?] for help or [C-h i] show the manual And if user type ?, a popup (like in magit) show all possibles actions with their corresponding key.

[abo-abo]

This was already added recently. Update and press ?.

[ghost]

Maybe be a little more new friendly by adding this to minibuffer when user call ace-window function: Select a window [1--3] or an action, type [?] for help or [C-h i] show the manual ?

[abo-abo]

The problem here is that I don't want to see that message as an experienced user.