Update readme

Author: AlexVanderbist

README.md

@@ -84,6 +84,10 @@ $users = QueryBuilder::for(User::class)
 
 [Read more about appending attributes.](https://docs.spatie.be/laravel-query-builder/v2/features/appending-attributes/)
 
+## ⚠ Possible breaking changes from v2 to v3
+
+Please check the [CHANGELOG](CHANGELOG.md) for some notes regarding upgrading from v2 to v3.
+
 ## Support us
 
 Learn how to create a package like this one, by watching our premium video course:

UPGRADING.md

@@ -2,6 +2,14 @@
 
 Because there are many breaking changes an upgrade is not that easy. There are many edge cases this guide does not cover. We accept PRs to improve this guide.
 
+## From v2 to v3
+
+Possible changes in this version due to internal changes.
+
+The package's `Spatie\QueryBuilder\QueryBuilder` class no longer extends Laravel's `Illuminate\Database\Eloquent\Builder`. This means you can no longer pass a `QueryBuilder` instance where a `Illuminate\Database\Eloquent\Builder` instance is expected. However, all Eloquent method calls get forwarded to the internal `Illuminate\Database\Eloquent\Builder`.
+
+Using `$queryBuilder->getEloquentBuilder()` you can access the internal `Illuminate\Database\Eloquent\Builder`.
+
 ## From v1 to v2
 
 There are a lot of renamed methods and classes in this release. An advanced IDE like PhpStorm is recommended to rename these methods and classes in your code base. Use the refactor -> rename functionality instead of find & replace.