Add default code reviewers into OWNERS

Bug: 33166666
Test: gerrit uploader
Change-Id: If0ce4d4f90335a84af89683538fa03b9c0745444
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..7529cb9
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1 @@
+include platform/system/core:/janitors/OWNERS