Add API docs for constraint module

src/ifcopenshell-python/ifcopenshell/api/constraint/add_objective.py

@@ -20,11 +20,29 @@ import ifcopenshell
 
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(self, file):
+        """Add a new objective constraint
+
+        Parametric constraints may be defined by the user. The constraint is defined
+        by first creating an objective describing the purpose of the constraint and
+        whether it is a hard or soft constraint. Later on, metrics may be added to
+        check whether the constraint has been met by connecting it to properties and
+        quantities. See ifcopenshell.api.constraint.add_metric for more information.
+
+        :return: The newly created IfcObjective entity
+        :rtype: ifcopenshell.entity_instance.entity_instance
+
+        Example::
+
+            # Create a new objective for code compliance requirements
+            objective = ifcopenshell.api.run("constraint.add_objective", model)
+            objective.ConstraintGrade = "ADVISORY"
+            objective.ObjectiveQualifier = "CODECOMPLIANCE"
+            # Note: the objective right now is purely qualitative and for
+            # information purposes. You may wish to add quantiative metrics.
+        """
         self.file = file
         self.settings = {}
-        for key, value in settings.items():
-            self.settings[key] = value
 
     def execute(self):
         return self.file.create_entity(