Devx improvements

[GioLogist]

Improved DevX with Yarn Workspaces

• Setup yarn workspaces, so that example package can import relay-nextjs directly
• Update dependencies in relay-nextjs (dev only)
• Update typescript with live reloading, for faster devx
• Update docs with "contributing" instructions for developing locally to contribute

---

Contributing

If you'd like to contribute to this package, developing locally is now as simple as:

1. Run yarn from the root of this package
2. Start the live reloader for the package cd packages/relay-nextjs && yarn build-w
3. In a separate terminal strt the example app: cd example && yarn dev

Now, when you make any changes in packages/relay-nextjs, they will instantly be reflected in the example app.