Make syntax highlighting explicit in docs

src/ifcopenshell-python/ifcopenshell/api/unit/assign_unit.py

@@ -40,7 +40,9 @@ class Usecase:
         :return: The IfcUnitAssignment element
         :rtype: ifcopenshell.entity_instance.entity_instance
 
-        Example::
+        Example:
+
+        .. code:: python
 
             # You need a project before you can assign units.
             ifcopenshell.api.run("root.create_entity", model, ifc_class="IfcProject")