Add ModelChainResults to classes section of api.rst

Author: wfvining

docs/sphinx/source/api.rst

@@ -23,6 +23,7 @@ corresponding procedural code.
    pvsystem.Array
    tracking.SingleAxisTracker
    modelchain.ModelChain
+   modelchain.ModelChainResult
 
 
 Solar Position

pvlib/modelchain.py

@@ -265,6 +265,7 @@ def get_orientation(strategy, **kwargs):
 
 @dataclass
 class ModelChainResult:
+    """Contains the results of running a ModelChain."""
     T = TypeVar('T')
     PerArray = Union[T, Tuple[T, ...]]
     # system-level information