Using internal regulator DVDD pin to power up external devices
Yes - you understood it correctly. The internal regulator needs external decoupling capacitor for stability, so the voltage is available on a pin and as a nice side effect you can use up to 30mA from that regulator.
Assume 2V forward voltage of the diode, aim for 10mA (should be bright enough) and apply Ohm's law: R = U / I = (3.3 - 2.0)[V] / 0.01 [A] = 130 [Ohm]. A 150 Ohm resistor should be good enough. Or use any of the available calculators.