add notices about distributed files not under the EO copyright

COPYING

@@ -1,5 +1,15 @@
-Docbow is entirely under the copyrigh of Entr'ouvert and distributed
-under the license AGPLv3.
+Docbow is under the copyright of Entr'ouvert and distributed under the terms of
+the GNU Affero General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any later
+version.
+
+Docbow also sports unmodified copies of external softwares or data files:
+- the jQuery and jQuery UI libraries which are distributed by their respective
+  authors under the MIT or GPL licences;
+- allkeys.txt, a data file from the Unicode project is under MIT licences.
+  See http://unicode.org/copyright.html;
+- pyuca by James Tauber is under MIT licences.
+
 
                     GNU AFFERO GENERAL PUBLIC LICENSE
                        Version 3, 19 November 2007