Clarify how to use Environment Variables on Vercel (#20708)

Updates the env documentation to mention `.vercelignore` when using the Vercel CLI. Also clears up parts of the other paragraphs and updates the links as these topics now have dedicated pages in the Vercel docs.

docs/basic-features/environment-variables.md

@@ -109,16 +109,18 @@ Next.js allows you to set defaults in `.env` (all environments), `.env.developme
 
 ## Environment Variables on Vercel
 
-When deploying on [Vercel](https://vercel.com) you can configure secrets in the [Environment Variables](https://vercel.com/docs/v2/build-step#environment-variables) section of the project in the Vercel dashboard.
+When deploying your Next.js application to [Vercel](https://vercel.com), Environment Variables can be configured [in the Project Settings](https://vercel.com/docs/environment-variables).
 
-You can still use `.env`, `.env.development` and `.env.production` to add defaults.
+All types of Environment Variables should be configured there. Even Environment Variables used in Development – which can be [downloaded onto your local device](https://vercel.com/docs/environment-variables#development-environment-variables) afterwards.
 
-If you've configured [Development Environment Variables](https://vercel.com/docs/v2/build-step#development-environment-variables) you can pull them into a `.env.local` for usage on your local machine using the following command:
+If you've configured [Development Environment Variables](https://vercel.com/docs/environment-variables#development-environment-variables) you can pull them into a `.env.local` for usage on your local machine using the following command:
 
 ```bash
 vercel env pull .env.local
 ```
 
+When using the Vercel CLI to deploy make sure you add a [`.vercelignore`](https://vercel.com/guides/prevent-uploading-sourcepaths-with-vercelignore?query=vercelignore#allowlist) that includes files that should not be uploaded, generally these are the same files included in `.gitignore`.
+
 ## Test Environment Variables
 
 Apart from `development` and `production` environments, there is a 3rd option available: `test`. In the same way you can set defaults for development or production environments, you can do the same with `.env.test` file for testing environment (though this one is not so common as the previous two).