preseed: Add non-free and contrib

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
diff --git a/preseed.cfg b/preseed.cfg
index 8162fa5..7137367 100644
--- a/preseed.cfg
+++ b/preseed.cfg
@@ -289,8 +289,8 @@
 
 ### Apt setup
 # You can choose to install non-free and contrib software.
-#d-i apt-setup/non-free boolean true
-#d-i apt-setup/contrib boolean true
+d-i apt-setup/non-free boolean true
+d-i apt-setup/contrib boolean true
 # Uncomment this if you don't want to use a network mirror.
 #d-i apt-setup/use_mirror boolean false
 # Select which update services to use; define the mirrors to be used.