docs: SDK design document
# Description
We need to really flesh out what all is going to be included in the MVP for this SDK. There's a lot we _could_ include that doesn't _need_ to be included, at least not for a first release.
# Proposal
- [x] Create SDK design document in `docs/src/content/docs/reference/requirements.md`
- [x] Baseline things to include:
- [ ] Spoke.Zone Client (all features...? How much of the API should be supported?)
- [ ] CAN flasher library
- [ ] Others TBD
issue