Initial "janitors" owner group.

This will let us clean up a lot of external/*/OWNERS files by
indirecting them through here.

Test: N/A
Change-Id: Ieda353b78deeb94baeab6306b6a734b63484d351
diff --git a/janitors/OWNERS b/janitors/OWNERS
new file mode 100644
index 0000000..0610b41
--- /dev/null
+++ b/janitors/OWNERS
@@ -0,0 +1,4 @@
+# OWNERS file for projects that don't really have owners so much as volunteer janitors.
+enh@google.com
+hhb@google.com
+narayan@google.com