README: Document how devices should referred to in docker-compose.yml

[doronbehar]

This is not common knowledge.. I had to use GitHub's search to find out how my balena Fin should be referred to, and I reached #12 ..

[ghost]

An error occurred whilst building your landr site preview:

{
  "name": "Error",
  "message": "Command failed with code 1: /usr/src/app/node_modules/react-static/bin/react-static build --config=/usr/src/app/lib/static.config.js",
  "stack": "Error: Command failed with code 1: /usr/src/app/node_modules/react-static/bin/react-static build --config=/usr/src/app/lib/static.config.js\n    at Object.exports.run (/usr/src/app/lib/build-runner.js:135:11)\n    at async build (/usr/src/app/bot/index.js:105:19)\n    at async /usr/src/app/bot/index.js:158:23"
}