feat(pkg-support): Add `pkg` entry to package.json

[bengreenier]

This allows pkg to include the static assets in the snapshot filesystem, addressing #28.

Checklist

• [x] run npm run test and npm run benchmark (there is no benchmark script?)
• [ ] tests and/or benchmarks are included (don't feel these are relevant, omitting)
• [ ] documentation is changed or added (don't feel these are needed, omitting)
• [x] commit message and code follows the Developer's Certification of Origin and the Code of conduct