Add API docs for constraint module

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

@@ -18,11 +18,29 @@
 
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(self, file, metric=None, attributes=None):
+        """Edit the attributes of a metric
+
+        For more information about the attributes and data types of an
+        IfcMetric, consult the IFC documentation.
+
+        :param metric: The IfcMetric you want to edit.
+        :type metric: ifcopenshell.entity_instance.entity_instance
+        :param attributes: a dictionary of attribute names and values.
+        :type attributes: dict, optional
+        :return: None
+        :rtype: None
+
+        Example::
+
+            objective = ifcopenshell.api.run("constraint.add_objective", model)
+            metric = ifcopenshell.api.run("constraint.add_metric", model,
+                objective=objective)
+            ifcopenshell.api.run("constraint.edit_metric", model,
+                metric=metric, attributes={"ConstraintGrade": "HARD"})
+        """
         self.file = file
-        self.settings = {"metric": None, "attributes": {}}
-        for key, value in settings.items():
-            self.settings[key] = value
+        self.settings = {"metric": metric, "attributes": attributes or {}}
 
     def execute(self):
         for name, value in self.settings["attributes"].items():