Specify more precisely where to include repository key on init

[wade-cheng]

Doc request:

  × Github CI support requires you to specify the URL of your repository
  help: Set the repository = "https://github.com/..." key in these manifests:
        /home/saffron/Documents/projects/compile-typst-site/Cargo.toml

This should (personally) preferably mention the specific [package] table within the cargo toml.

[mistydemeo]

Good callout! I can look into making the change.