Mention an exception in load_settings

This is caught internally - but it seemed easier to add an explanation in the docstring than to exempt it and document that. This isn't a user-facing function anyway.

Author: rwb27

src/labthings_fastapi/thing.py

@@ -200,6 +200,10 @@ def load_settings(self) -> None:
             Note that no notifications will be triggered when the settings are set,
             so if action is needed (e.g. updating hardware with the loaded settings)
             it should be taken in ``__enter__``.
+
+        :raises TypeError: if the JSON file does not contain a dictionary. This is
+            handled internally and logged, so the exception doesn't propagate
+            outside of the function.
         """
         setting_storage_path = self._thing_server_interface.settings_file_path
         thing_name = type(self).__name__