bug#44894: Highly related line number articles should mention each other

[積丹尼 Dan Jacobson]

(info "(emacs) Optional Mode Line") says

      The current line number of point appears in the mode line when Line
   Number mode is enabled.  Use the command ‘M-x line-number-mode’ to turn
   this mode on and off; normally it is on.  The line number appears after
   the buffer percentage POS, with the letter ‘L’ to indicate what it is.

(info "(emacs) Display Custom")

      If you want to have Emacs display line numbers for every line in the
   buffer, customize the buffer-local variable ‘display-line-numbers’; it
   is ‘nil’ by default.  This variable can have several different values to
   support various modes of line-number display:

OK, but each should also mention

   By the way, see also ...

referring to the other!

emacs-version "27.1"