feat: class docstring overrides default description from __schema__, f…

…ixes antonagestam#238

src/phantom/schema.py

@@ -32,8 +32,11 @@ def __modify_schema__(cls, field_schema: dict) -> None:
         :func:`__schema__() <phantom.Phantom.__schema__>` to provide custom schema
         representations for phantom types.
         """
+        schema = cls.__schema__()
+        if cls.__doc__ is not None:
+            schema["description"] = cls.__doc__
         field_schema.update(
-            {key: value for key, value in cls.__schema__().items() if value is not None}
+            {key: value for key, value in schema.items() if value is not None}
         )
 
     @classmethod
@@ -44,6 +47,9 @@ def __schema__(cls) -> Schema:
         for more information. This hook differs to pydantic's ``__modify_schema__()``
         and expects subclasses to instantiate new dicts instead of mutating a given one.
 
+        Note that the docstring attached to a phantom type class, if present,
+        will override any description that is defined in `__schema__()`.
+
         Example:
 
         .. code-block:: python