Add default code reviewers into OWNERS

Bug: 33166666
Test: gerrit uploader
Change-Id: I48a0129f2ca58127d932f55a6448c4ba00e565e7
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..3cf3301
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,3 @@
+# Default code reviewers picked from top 3 or more developers.
+# Please update this list if you find better candidates.
+luum@google.com