### What needs to get done Display better validation error messages to the user when platforms are not correctly defined. This is a follow-up to # ### Why it needs to get done This is the current validation error message: ``` wheelcraft internal error: ValidationError(model='BuildPlanner', errors=[{'loc': ('platforms', 'build-on'), 'msg': 'value is not a valid list', 'type': 'type_error.list'}]) ```