[Exit the Matrix]

Beam down a camera crew to document the incident, then market it as a science fiction movie trilogy?

 But in all seriousness, I think that interference would be unwise regardless of the Prime Directive. There are just too many unknowns about this situation. Where did the machines on this world come from? Do they have some ulterior motive besides using the native population for computing power (were the machines at one point the slaves, perhaps)? Would they really be better off free and either at war or having to start anew from the ground up? Unless I saw direct evidence of harm being inflicted on the aliens, there's not enough information and too many value judgments necessary to make a logical choice for the good of all involved.