docs: adapt validate docs

docs/source/howtos/2 Validating Scenes.rst

@@ -17,12 +17,14 @@ For the validation you need 2 things: the scene and the project specific ontholo
 The onthology should be provided by your project partner. It is a .yaml-file listing all classes and their attributes.
 
 .. code-block:: python
+    import json
+    from pathlib import Path
 
     from raillabel_providerkit import validate
-    import raillabel
 
-    scene = raillabel.load("path/to/scene.json")
+    with Path("path/to/scene.json").open() as scene_file:
+        scene_dict = json.load(scene_file)
 
-    assert validate(scene, "path/to/onthology.yaml") == []
+    assert validate(scene_dict) == []
 
 If this code does not raise any errors, you are good to go. If it does, read the content of the list `validate` returns carefully. It should tell you where the errors are. If you are unsure, contact your project partner or raise an issue on GitHub.