Add API docs for drawing module

src/ifcopenshell-python/ifcopenshell/api/drawing/unassign_product.py

@@ -21,14 +21,38 @@ import ifcopenshell.api
 
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(self, file, relating_product=None, related_object=None):
+        """Unassigns a product and an object (typically an annotation)
+
+        Smart annotation objects can be associated with products so that they
+        can annotate attributes and properties. This function lets you remove
+        the association, so that you may change the assocation with another
+        object later or leave the annotation as a "dumb" annotation.
+
+        :param relating_product: The IfcProduct the object is related to
+        :type relating_product: ifcopenshell.entity_instance.entity_instance
+        :param related_object: The object (typically IfcAnnotation) that the
+            product is related to
+        :type related_object: ifcopenshell.entity_instance.entity_instance
+        :return: The created IfcRelAssignsToProduct relationship
+        :rtype: ifcopenshell.entity_instance.entity_instance
+
+        Example::
+
+            furniture = ifcopenshell.api.run("root.create_entity", model, ifc_class="IfcFurniture")
+            annotation = ifcopenshell.api.run("root.create_entity", model, ifc_class="IfcAnnotation")
+            ifcopenshell.api.run("drawing.assign_product", model,
+                relating_product=furniture, related_object=annotation)
+
+            # Let's change our mind and remove the relationship
+            ifcopenshell.api.run("drawing.unassign_product", model,
+                relating_product=furniture, related_object=annotation)
+        """
         self.file = file
         self.settings = {
-            "relating_product": None,
-            "related_object": None,
+            "relating_product": relating_product,
+            "related_object": related_object,
         }
-        for key, value in settings.items():
-            self.settings[key] = value
 
     def execute(self):
         for rel in self.settings["related_object"].HasAssignments or []: