docker: update README.md (pterodactyl#4388)

Author: slimshizn

.github/docker/README.md

@@ -27,7 +27,7 @@ docker-compose exec panel php artisan p:user:make
 ## Environment Variables
 There are multiple environment variables to configure the panel when not providing your own `.env` file, see the following table for details on each available option.
 
-Note: If your `APP_URL` starts with `https://` you need to provide an `LETSENCRYPT_EMAIL` as well so Certificates can be generated.
+Note: If your `APP_URL` starts with `https://` you need to provide an `LE_EMAIL` as well so Certificates can be generated.
 
 | Variable            | Description                                                                    | Required |
 | ------------------- | ------------------------------------------------------------------------------ | -------- |