DEVELOPERS: add Christian Stewart to balena-engine package

Signed-off-by: Christian Stewart <christian@paral.in>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit fc644ed3be1ae52bf883f93083fc96f9fe1f2ee4)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

DEVELOPERS

@@ -531,6 +531,7 @@ N:	Christian Kellermann <christian.kellermann@solectrix.de>
 F:	package/python-pylibftdi/
 
 N:	Christian Stewart <christian@paral.in>
+F:	package/balena-engine/
 F:	package/batman-adv/
 F:	package/catatonit/
 F:	package/cni-plugins/