bug#27230: eldoc doc

[Charles A. Roelli]

From the top of eldoc.el:

;; One useful way to enable this minor mode is to put the following in your
;; .emacs:
;;
;;      (add-hook 'emacs-lisp-mode-hook 'eldoc-mode)
;;      (add-hook 'lisp-interaction-mode-hook 'eldoc-mode)
;;      (add-hook 'ielm-mode-hook 'eldoc-mode)
;;      (add-hook 'eval-expression-minibuffer-setup-hook 'eldoc-mode)

In 25.2, none of these lines are needed.  Maybe
these lines could be replaced with a mention of global-eldoc-mode,
and how the "globalized" minor mode and eldoc-mode interact (not sure
how they do).

Also, most of the functions in eldoc have no docstring (seems ironic).
Would there be any interest in a patch to fix that?