Ambiguous TODO in ff_derive

[CPerezz]

In https://github.com/zkcrypto/ff/blob/e853770f4843e47cd5e07330140b5bd1cdfc9f11/ff_derive/src/lib.rs#LL130C27-L130C36 is mentioned that the generator should be computed by the code instead of being given by the macro caller.

The thing is that I'm not sure how are we supposed to pick a generator when we can have an insane amount of possible valid choices. Is there any logic like picking the lowest or similar that you were thinking on applying here?