doc: Add section to attract more people towards the GNU project

[Bruno Haible]

On the gnu-prog-discuss mailing list there is agreement that it's a good idea
to have a section that invites the reader to read more about GNU and potentially
join GNU. Several people, including RMS, shaped the text.

In most packages, it's in the README. But Gnulib's documentation is entirely
in TeXinfo format. Therefore it's to be added there.

The only question were was where exactly to add this text. I chose to put it
at the end of the first chapter. Possibly there are better suggestions?


2022-06-05  Bruno Haible  <bruno@clisp.org>

        doc: Add section to attract more people towards the GNU project.
        Inspired by a suggestion from José E. Marchesi <jemarch@gnu.org> on
        the gnu-prog-discuss mailing list.
        * doc/join-gnu.texi: New file.
        * doc/gnulib-readme.texi: Include it.

diff --git a/doc/gnulib-readme.texi b/doc/gnulib-readme.texi
index 9032b1498c..492572799c 100644
--- a/doc/gnulib-readme.texi
+++ b/doc/gnulib-readme.texi
@@ -15,6 +15,7 @@
 * Contributing to Gnulib::
 * Portability guidelines::
 * High Quality::
+* Joining GNU::
 @end menu
 
 @node Gnulib Basics
@@ -583,3 +584,5 @@ libraries (@code{libstdc++} and @code{libubsan}) to be 
linked
 statically rather than dynamically, though this typically bloats the
 executable and the remaining extra libraries are still linked
 dynamically.
+
+@include join-gnu.texi
diff --git a/doc/join-gnu.texi b/doc/join-gnu.texi
new file mode 100644
index 0000000000..deacc451b6
--- /dev/null
+++ b/doc/join-gnu.texi
@@ -0,0 +1,24 @@
+@c Copyright (C) 2021--2022 Free Software Foundation, Inc.
+
+@c Permission is granted to copy, distribute and/or modify this document
+@c under the terms of the GNU Free Documentation License, Version 1.3 or
+@c any later version published by the Free Software Foundation; with no
+@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
+@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>.
+
+@node Joining GNU
+@section Join the GNU Project
+
+GNU Gnulib is part of the GNU Operating System, developed by the GNU Project.
+
+If you are the author of an awesome program and want to join us in
+writing Free (libre) Software, please consider making it an official
+GNU program and become a GNU Maintainer.  Instructions on how to do
+this are @url{https://www.gnu.org/help/evaluation, here}.
+We are looking forward to hacking with you!
+
+Don't have a program to contribute?  Look at all the
+@url{https://www.gnu.org/help/help.html, other ways to help}.
+
+And to learn more about Free (libre) Software in general, please read
+and share @url{https://gnu.org/philosophy/free-sw.html, this page}.