Add section/priority for source package

Change-Id: I5aee465c9939731b5808695e692c8cdfa12cc413
diff --git a/debian/control b/debian/control
index 251a858..971eee3 100644
--- a/debian/control
+++ b/debian/control
@@ -1,4 +1,6 @@
 Source: aiy-board-keyring
+Section: misc
+Priority: optional
 Maintainer: AIY Projects <support-aiyprojects@google.com>
 Build-Depends: debhelper, gnupg