Function help_string 

pub fn help_string(binds: &Bindings, opener: &Opener) -> String

Creates the help String from keybindings. If multiple keybindings are bound to the same action, the last one is displayed. If an action displayed in help isn’t bound to a key, the formating won’t be possible. We use the default keybindings instead. If it doesn’t work, we return an empty string.