[pan] README.org: prefer gmime3 over deprecated gmime2

[Dominique Dumont <ddumont src gnome org>]

commit e42d3fffb4eb514c0aea23a21e11f66dc3102764
Author: Dominique Dumont <dod debian org>
Date:   Mon Oct 18 19:20:44 2021 +0200

    README.org: prefer gmime3 over deprecated gmime2

 README.org | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/README.org b/README.org
index 2e0ed78..9dad7d2 100644
--- a/README.org
+++ b/README.org
@@ -73,7 +73,7 @@ Pan requires these libraries:
 - [[http://developer.gnome.org/glib/][GLib]] 2.17.6 or higher
   (optionally GLib 2.26.0 or higher to support multiple Pan instances)
 - [[http://www.gtk.org/][GTK+]] 2.16.0 or higher (optionally GTK+ 3.0.0 or higher)
-- [[https://gitlab.gnome.org/GNOME/gmime][GMime]] 2.6.20 or higher (optionally with PGP cryptography support)
+- [[http://spruce.sourceforge.net/gmime/][GMime]] 3.0.0 or higher (optionally with PGP cryptography support)
 
 The following libraries add extra features but are optional:
 
@@ -91,9 +91,12 @@ The following libraries add extra features but are optional:
 The following libraries are experimental and not suitable for any use
 other than testing. Use at your own risk:
 
-- [[http://spruce.sourceforge.net/gmime/][GMime]] 3.0.0 or higher (optionally with PGP cryptography support)
 - [[https://webkitgtk.org/][WebKitGTK+]] 1.8.1 or higher for embedded HTML
 
+The following librairies are deprecated and will be removed in future
+releases:
+- [[https://gitlab.gnome.org/GNOME/gmime][GMime]] 2.6.20 or higher (optionally with PGP cryptography support)
+
 Run the following command to get a list of all options that you can
 enable or disable at configure (or autogen) time: