Add default code reviewers into OWNERS

Bug: 33166666
Test: gerrit uploader
Change-Id: Id343ebd8648cbba9f0973ecc0d66289de2878469
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..7e70526
--- /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.
+enh@google.com
+narayan@google.com
+justinyun@google.com