Or set the API token manually:
echo 'NUXT_ENV_DATOCMS_API_TOKEN=abc123' >> .env
# install dependencies
$ npm install
# serve with hot reload at localhost:3000
$ npm run dev
# build for production and launch server
$ npm run build
$ npm run start
# generate static project
$ npm run generate
For detailed explanation on how things work, check out Nuxt.js docs.