Severity: minor

In `(elisp) Documentation Tips', we read:

     It is not practical to use ‘\\[...]’ very many times, because
     display of the documentation string will become slow.  So use this
     to describe the most important commands in your major mode, and
     then use ‘\\{...}’ to display the rest of the mode’s keymap.

When testing this on my machine on a docstring with a large number of
substitutions (107), I get the following (in "emacs -Q"):

(progn (require 'ibuffer)
       (let ((times 100))
         (/ (car (benchmark-run
                     times (documentation 'ibuffer-mode)))
            times)))

    => 0.00499586008

When I increase the number of substitutions in that docstring to around 1000 (by
duplicating the docstring 10 times), I get:

    => 0.05029239337

This is 10 times slower, but still fast enough that it does not matter much.
It also suggests that this is O(N) in time.

My conclusion is that the above recommendation in `(elisp) Documentation Tips'
is irrelevant these days, and I suggest to remove it.

Please see the attached patch.