Add documentation for cost module

src/ifcopenshell-python/ifcopenshell/api/cost/remove_cost_item.py

@@ -20,11 +20,26 @@ import ifcopenshell.api
 
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(self, file, cost_item=None):
+        """Removes a cost item
+
+        All associated relationships with the cost item are also removed,
+        however the related resources, products, and tasks themselves are
+        retained.
+
+        :param cost_item: The IfcCostItem entity you want to remove
+        :type cost_item: ifcopenshell.entity_instance.entity_instance
+        :return: None
+        :rtype: None
+
+        Example::
+
+            schedule = ifcopenshell.api.run("cost.add_cost_schedule", model)
+            item = ifcopenshell.api.run("cost.add_cost_item", model, cost_schedule=schedule)
+            ifcopenshell.api.run("cost.remove_cost_item", model, cost_item=item)
+        """
         self.file = file
-        self.settings = {"cost_item": None}
-        for key, value in settings.items():
-            self.settings[key] = value
+        self.settings = {"cost_item": cost_item}
 
     def execute(self):
         # TODO: do a deep purge