[gedit] contributing: add an intro

[Sébastien Wilmet <swilmet src gnome org>]

commit 2b65b97295a759e25c69934d79e4f394b27fb8ff
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Mon Aug 26 09:47:15 2019 +0200

    contributing: add an intro
    
    Inspired by the content from the old gedit website:
    https://projects-old.gnome.org/gedit/developers.html

 CONTRIBUTING | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/CONTRIBUTING b/CONTRIBUTING
index aca3c0426..bc681dd24 100644
--- a/CONTRIBUTING
+++ b/CONTRIBUTING
@@ -1,6 +1,17 @@
 How to contribute to gedit
 ==========================
 
+gedit development relies on voluntary contributions and everyone is invited to
+help.
+
+If you are interested in helping us to improve gedit, please contact the
+developers on IRC and/or send a message to the gedit mailing list and offer your
+help. See the “Getting in Touch” section on the
+[gedit wiki page](https://wiki.gnome.org/Apps/Gedit).
+
+Getting started with gedit software development
+-----------------------------------------------
+
 See the file `docs/gedit-development-getting-started.md` and the rest of this
 file.