What resistor values should I use with this boost DC-DC converter IC?
Leave it to ST to publish a crap datasheet...

Look at the block diagram.


It shows that putting resistors as shown in the application circuit forms a noninverting amplifier with OTA*. There is also a feedback spec.


You can use that feedback voltage and your desired output voltage to calculate the voltage divider values. 

*OTA usually stands for operation transconductance amplifier. If that is what it actually is, then this answer is wrong. If I was designing with this part, I would reverse engineer an eval board circuit to confirm this hypothesis.