Newbie question: how to add <c> (Ctrl) as a which-key trigger?

[joost8]

I am using which-key as configured by the nvim-kickstart repo (https://github.com/nvim-lua/kickstart.nvim) and am loving it so far. I have started adding and keymaps for specific functionality.

How can I have which-key pop up when I type for example the Ctrl or Alt keys? Would that be configured in opts and could you provide an example?