Describe the fact that first GET collectionOperation is used for resourceClass IRI (#407)

* Add note about the fact that first GET collectionOperation is used for resourceClass IRI

* Update operations.md

Author: Benjamin Rau

core/operations.md

@@ -485,6 +485,8 @@ automatically instantiated and injected, without having to declare it explicitly
 In the following example, the built-in `GET` operation is registered as well as a custom operation called `special`.
 The `special` operation reference the Symfony route named `book_special`.
 
+Note: API Platform uses the first operation (with `GET` method) defined in `collectionOperations` to generate the IRI for this resource class. This means that as long as you dont want to overwrite the IRI for this resource class by intention, the default collection operation associated with the `GET` method should be the first operation defined inside collection operations.
+
 ```php
 <?php
 // src/Entity/Book.php