fix serialization

Author: dunglas

core/serialization.md

@@ -8,7 +8,7 @@ API Platform embraces and extends the Symfony Serializer Component to transform
 
 The main serialization process has two stages:
 
-![Serializer workflow](images/SerializerWorkflow.png)
+![Serializer workflow](/docs/core/images/SerializerWorkflow.png)
 
 > As you can see in the picture above, an array is used as a man-in-the-middle. This way, Encoders will only deal with turning specific formats into arrays and vice versa. The same way, Normalizers will deal with turning specific objects into arrays and vice versa.
 -- [The Symfony documentation](https://symfony.com/doc/current/components/serializer.html)