Write docs for system API module

src/ifcopenshell-python/ifcopenshell/api/system/edit_system.py

@@ -18,11 +18,30 @@
 
 
 class Usecase:
-    def __init__(self, file, **settings):
+    def __init__(self, file, system=None, attributes=None):
+        """Edits the attributes of an IfcSystem
+
+        For more information about the attributes and data types of an
+        IfcSystem, consult the IFC documentation.
+
+        :param system: The IfcSystem entity you want to edit
+        :type system: ifcopenshell.entity_instance.entity_instance
+        :param attributes: a dictionary of attribute names and values.
+        :type attributes: dict, optional
+        :return: None
+        :rtype: None
+
+        Example::
+
+            # A completely empty distribution system
+            system = ifcopenshell.api.run("system.add_system", model)
+
+            # Change the name of the system to "HW" for Hot Water
+            ifcopenshell.api.run("system.edit_system", model, system=system, attributes={"Name": "HW"})
+        """
+
         self.file = file
-        self.settings = {"system": None, "attributes": {}}
-        for key, value in settings.items():
-            self.settings[key] = value
+        self.settings = {"system": system, "attributes": attributes or {}}
 
     def execute(self):
         for name, value in self.settings["attributes"].items():