This PR updates the `with-userbase` example with the following changes:

- Removes the `vercel.json` file, this is no longer needed with [recent changes](https://vercel.com/docs/v2/build-step#environment-variables).
- Changes the URL of the Deploy Button to use `?env`, `?envLink`, and `?envDescription` query strings, these prompt for environment variables upon import.
- Updates the instructions to reflect the changes made to the import and deployment process.