Add comments for update_expired_feeds in db_block

Author: abitmore

libraries/chain/db_block.cpp

@@ -536,8 +536,8 @@ void database::_apply_block( const signed_block& next_block )
    clear_expired_transactions();
    clear_expired_proposals();
    clear_expired_orders();
-   update_expired_feeds();
-   update_core_exchange_rates();
+   update_expired_feeds();       // this will update expired feeds and some core exchange rates
+   update_core_exchange_rates(); // this will update remaining core exchange rates
    update_withdraw_permissions();
 
    // n.b., update_maintenance_flag() happens this late