Remove unnecessary `object` base class in docs (#10366).

Also add a note about inheritance from `object` being default.
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst
index 95d5705..1622133 100644
--- a/Doc/reference/compound_stmts.rst
+++ b/Doc/reference/compound_stmts.rst
@@ -561,7 +561,16 @@
 A class definition is an executable statement.  The inheritance list usually
 gives a list of base classes (see :ref:`metaclasses` for more advanced uses), so
 each item in the list should evaluate to a class object which allows
-subclassing.
+subclassing.  Classes without an inheritance list inherit, by default, from the
+base class :class:`object`; hence, ::
+
+   class Foo:
+       pass
+
+is equivalent to ::
+
+   class Foo(object):
+       pass
 
 The class's suite is then executed in a new execution frame (see :ref:`naming`),
 using a newly created local namespace and the original global namespace.