Add local macOS VM dev machine setup instructions
Add local macOS VM dev machine setup instructions

Contributes towards #825

Squashed commit messages:
- Clarify that new macOS instructions pertain to VMware Fusion
- Add note per feedback in https://github.com/firecracker-microvm/firecracker/pull/940#issuecomment-472493419

Signed-off-by: 4fcf238f309c34dd3a886f1fc54a610e90e66020@mail.co.de)

firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker,firecracker-microvm/firecracker