Retireve docstirng form base classes (Closes #3140)

doc/ext/autodoc.rst

@@ -393,6 +393,16 @@ There are also new config values that you can set:
    If ``False`` is given, autodoc forcely suppresses the error if the imported
    module emits warnings.  By default, ``True``.
 
+.. confval:: autodoc_inherit_docstrings
+
+   This value controls the docstrings inheritance.
+   If set to True the cocstring for classes or methods, if not explicitly set,
+   is inherited form parents.
+
+   The default is ``True``.
+
+   .. versionadded:: 1.7
+
 Docstring preprocessing
 -----------------------