This repository seems out of sync with the CodeLab documentation.

https://firebase.google.com/codelabs/firestore-web?hl=ja#5

I was following this tutorial and felt uncomfortable as I was learning.
Apparently, this tutorial instructs you to run `firebase use --add` or `firebase emulators:start --only hosting` in the top-level directory of the repository, but this command is not actually valid.

After trying various things, it seems that this tutorial assumes that the commands are to be run in the `vanilla-js` directory.

Perhaps the tutorial documentation and the repository are out of sync.

I would like to suggest an improvement.