Add informational messages when indexing

backend-chests.lua

@@ -51,7 +51,8 @@ end
 local function update_index()
     print "Indexing started."
 	for n in pairs(inventories) do
-		update_index_for(n)
+        update_index_for(n)
+        print("Indexed", n)
 		sleep()
 	end
 	print "Indexing complete."