Add Étienne in the AUTHORS file

Étienne has done an enormous amount of development on the multi-page
renderer, and therefore should be mentionned in our AUTHORS file.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@enix.org>

AUTHORS

@@ -1,5 +1,6 @@
 David Decotigny <david@decotigny.fr>
 Frédéric Lehobey <frederic@lehobey.net>
+Étienne Loks <etienne.loks@peacefrogs.net>
 David Mentré <dmentre@linux-france.org>
 Maxime Petazzoni <maxime.petazzoni@bulix.org>
 Thomas Petazzoni <thomas.petazzoni@enix.org>