bug#59609: 29.0.50; [PATCH] Better advertise (Non-)GNU ELPA in emacs manual

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

> This sounds OK, but begs the question: what's short description of NonGNU
> ELPA?  Since we describe GNU ELPA, let's also describe the other one.  The
> purpose should IMO be to explain to the reader, or at least hint why we
> maintain two separate archives.

What do you think of the below?

diff --git a/doc/emacs/package.texi b/doc/emacs/package.texi
index cdfb45d2042..3ac7dc83a60 100644
--- a/doc/emacs/package.texi
+++ b/doc/emacs/package.texi
@@ -38,9 +38,17 @@ Packages
   By default, Emacs downloads packages from GNU ELPA
 (@url{https://elpa.gnu.org/}), a package archive maintained by the
 Emacs developers and hosted by the GNU project.  It also downloads
-packages from NonGNU ELPA (@url{https://elpa.nongnu.org/}).
-Optionally, you can also download packages from archives maintained by
-third parties.  @xref{Package Installation}.
+packages from NonGNU ELPA
+(@url{https://elpa.nongnu.org/}).@footnote{GNU ELPA contains GNU
+packages that are available for use with Emacs, but are distributed
+separately from Emacs itself, for reasons of space.  NonGNU ELPA
+contains a selection of third-party packages that can not be included
+in GNU ELPA because their copyright has not yet been assigned to the
+Free Software Foundation.  For more information, see
+@uref{https://www.gnu.org/licenses/why-assign.html, Why the FSF Gets
+Copyright Assignments from Contributors}.}  Optionally, you can also
+download packages from archives maintained by third parties.
+@xref{Package Installation}.

   For information about turning an Emacs Lisp program into an
 installable package, @xref{Packaging,,,elisp, The Emacs Lisp Reference