docs(migration): update to use new runtimeConfig (#4642)

Co-authored-by: Damian <48835293+DamianGlowala@users.noreply.github.com>

docs/content/migration/8.runtime-config.md

@@ -13,7 +13,7 @@ When referencing these variables within your components, you will have to use th
 
 ## Migration
 
-1. Add any environment variables you use in your app to your `publicRuntimeConfig` or `privateRuntimeConfig`.
+1. Add any environment variables that you use in your app to the `runtimeConfig` property of the `nuxt.config` file.
 1. Migrate `process.env` to `useRuntimeConfig` throughout the Vue part of your app.
 
 ## Example
@@ -25,9 +25,9 @@ import { defineNuxtConfig } from 'nuxt'
 
 export default defineNuxtConfig({
   runtimeConfig: {
-    secretKey: '', // variables that can only be accessed on server-side
+    secretKey: '', // variable that can only be accessed on the server side
     public: {
-      BASE_URL: process.env.BASE_URL || 'https://nuxtjs.org'
+      BASE_URL: process.env.BASE_URL || 'https://nuxtjs.org' // variable that can also be accessed on the client side
     }
   },
 })