Add system maintainers

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

pkg/system/MAINTAINERS

@@ -0,0 +1,2 @@
+Michael Crosby <michael@crosbymichael.com> (@crosbymichael)
+Guillaume J. Charmes <guillaume@docker.com> (@creack)