USB-C is a superset of USB-A/B, so you can use exactly the same simple protocol: A short of the D+ and D- pins, per USB Battery Charging.
For a USB-C sink, you don't even need any resistors beyond that, let alone USB-PD. For a USB-C source to be able to charge a legacy USB-B sink, all you need is a single 56 kOhm resistor.
For a USB-C sink, you don't even need any resistors beyond that, let alone USB-PD. For a USB-C source to be able to charge a legacy USB-B sink, all you need is a single 56 kOhm resistor.