Fix Node installation instructions

[syvb]

yarn install <package> no longer works to add a package:

$ yarn install nodejs-polars
yarn install v1.22.10
info No lockfile found.
error `install` has been replaced with `add` to add new dependencies. Run "yarn add nodejs-polars" instead.
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.

This changes the installation instructions to use the replacement, yarn add instead.

[universalmind303]

Thanks!