Hi @Mitch
The NNS team plans to add documentation to the developer doc portal on the day of proposal adoption to enable the 1-proposal feature. These docs will include a template sns.yml that contains some comments explaining each configuration field. Keep and eye on this topic to see when that documentation is going to go live. I plan to update it when the proposal is available and when its been adopted.
In the mean time, I’m happy to answer some questions 
- What is the
Principals: []field for.
This is currently a placeholder field. We intend to support aliasing principals in the near future for easier configuration. It can be left empty for now.
How does this vesting schedule parameter work?
start_time and duration are not part of the VestingSchedule structure.
The VestingSchedule is equivalent to to the NeuronBasketConstructionParameters but made more generic. This specifies how many SNS Neurons will be created for each participant in the decentralization swap. You specify the number of events (e.g. the number of neurons) and the interval of their dissolve delay.
- Where do you define a developer neuron? or is this no longer required with the 1 proposal method?
There is a new structure called the Distribution which contains a Neurons section. This is where you would specify the initial developer neurons.