Add default code reviewers into OWNERS

Bug: 33166666
Test: gerrit uploader
Change-Id: Ia522a8efab84706231d9ff2865634d09ee271374
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..ede8e13
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,5 @@
+# Default code reviewers picked from top 3 or more developers.
+# Please update this list if you find better candidates.
+stenning@google.com
+spaik@google.com
+ajchen@google.com