[Good first issue] The todo demo app setup guide is broken

It appears that the setup guide for the todo app is broken, but the app itself works (?). In particular, `yarn build` appears to delete the `__generated__/relay/queries.json` file and cause `yarn start` to fail with `ENOENT`.

One would need to:
* potentially upgrade the todo app to use the rust compiler (unless it does already?) and upgrade the config to use the new setup
* make the README accurate

If you choose to do this, please feel free to reach out to @statisticsftw on Twitter or join the Relay channel in the GraphQL discord (https://discord.gg/kFKSHK4V).

Thank you!