How to get an item into info menu?

[bill]

I have the info files for "Introduction to Programming in Emacs
Lisp" but no matter where I put those files, the corresponding menu
item (* Emacs Lisp Intro: (eintr).) never shows on the top menu
when I do C-h i in Emacs.  In every attempt I have placed the
file(s) in a directory mentioned in Info-default-directory-list.
I have tried both the single info file emacs-lisp-intro.info.gz
(from gnu.org) as well as the separate eintr*.gz files generated
by makeinfo and gzip from the contents of emacs-lisp-intro-texi.tar
(also from gnu.org).

Where's the documentation on how to do this?  I've looked everywhere.

Many thanks!

bill

P.S. In fact, searching in Info for the word "Info-default-directory-list"
yields nothing.  (It is ironic that the documentation system itself
is so poorly documented.  It's just like in the Spanish proverb
"In the blacksmith's house, wooden knife".)