Update with-userbase Example (#14100)

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.

examples/with-userbase/README.md

@@ -8,7 +8,7 @@ Deployed Demo: [https://next-userbase.now.sh](https://next-userbase.now.sh)
 
 Deploy the example using [Vercel](https://vercel.com):
 
-[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/import/project?template=https://github.com/vercel/next.js/tree/canary/examples/with-userbase)
+[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/import/git?s=https://github.com/vercel/next.js/tree/canary/examples/with-userbase&env=NEXT_PUBLIC_USERBASE_APP_ID&envDescription=encodeURI(The Userbase app ID, found in the Userbase dashboard.&envLink=https://v1.userbase.com/#))
 
 ## How to use
 
@@ -85,12 +85,6 @@ Your todo app should be up and running on [http://localhost:3000](http://localho
 
 You can deploy this app to the cloud with [Vercel](https://vercel.com/import?filter=next.js&utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).
 
-To deploy on Vercel, you need to set the environment variables using the [Vercel CLI](https://vercel.com/download) ([Documentation](https://vercel.com/docs/cli#commands/secrets)).
+To deploy on Vercel, you need to set the environment variable using the [Vercel dashboard](https://vercel.com/dashboard) ([Documentation](https://vercel.com/docs/v2/build-step#environment-variables)).
 
-Install [Vercel CLI](https://vercel.com/download), log in to your account from the CLI, and run the following command to add the environment variable. Replace <NEXT_PUBLIC_USERBASE_APP_ID> with the corresponding string in `.env.local`:
-
-```
-vercel secrets add userbase-app-id <NEXT_PUBLIC_USERBASE_APP_ID>
-```
-
-Then push the project to GitHub/GitLab/Bitbucket and [import to Vercel](https://vercel.com/import?filter=next.js&utm_source=github&utm_medium=readme&utm_campaign=next-example) to deploy.
+You can do this when importing your project by selecting the environment variables dropdown, and using a name of `NEXT_PUBLIC_USERBASE_APP_ID` with the [Userbase app ID](https://v1.userbase.com/#) as the value.

examples/with-userbase/package.json

 {
-  "name": "with-tailwindcss",
+  "name": "with-userbase",
   "version": "1.0.0",
   "scripts": {
     "dev": "next",

examples/with-userbase/vercel.json

-{
-  "build": {
-    "env": {
-      "NEXT_PUBLIC_USERBASE_APP_ID": "@userbase-app-id"
-    }
-  }
-}