reinstate function in docs

Author: RDaxini

docs/sphinx/source/reference/modelchain.rst

@@ -115,3 +115,12 @@ on the information in the associated :py:class:`~pvsystem.PVSystem` object.
    modelchain.ModelChain.infer_temperature_model
    modelchain.ModelChain.infer_losses_model
 
+Functions
+---------
+
+Functions for power modeling.
+
+.. autosummary::
+   :toctree: generated/
+
+   modelchain.get_orientation