[gnome-icon-theme-extras] add a paragraph about correct attribution to the license.

[Jakub Steiner <jimmac src gnome org>]

commit db7d8dd8fef73fbae7f194b2104438eada4d7706
Author: Jakub Steiner <jimmac gmail com>
Date:   Mon Mar 29 18:19:23 2010 +0200

    add a paragraph about correct attribution to the license.

 COPYING |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/COPYING b/COPYING
index dab313d..fc45d78 100644
--- a/COPYING
+++ b/COPYING
@@ -2,3 +2,6 @@ This work is licenced under the Creative Commons Attribution-Share Alike 3.0
 United States License. To view a copy of this licence, visit
 http://creativecommons.org/licenses/by-sa/3.0/ or send a letter to Creative
 Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA.
+
+When attributing the artwork, using "GNOME Project" is enough. 
+Please link to http://www.gnome.org where available.