bug#42709: Yes, mention C-g as one of the valid options

[積丹尼 Dan Jacobson]

Here we see the contents of the *Char Help* buffer
(that I couldn't copy so needed a screenshot. See my other bug today.)

It is made by
  C runs the command dired-do-copy (found in dired-mode-map), which is
  an interactive autoloaded compiled Lisp function in ‘dired-aux.el’.

I think it should also mention C-g, "to quit right away".

Sure, "The user is supposed to know that."

But, "He isn't sure it won't cause some damage, else if it were safe, it
would be listed."

emacs-version "26.3"