update co_flags docs

Author: methane

Doc/reference/datamodel.rst

@@ -1526,15 +1526,17 @@ positional arguments; bit ``0x08`` is set if the function uses the
 if the function is a generator. See :ref:`inspect-module-co-flags` for details
 on the semantics of each flags that might be present.
 
-Bits ``0x10``, ``0x1000``, and ``0x2000`` were used in earlier
-versions of Python.
+Future feature declarations (e.g. ``from __future__ import divisions``) also use
+in :attr:`~codeobject.co_flags` to indicate whether a code object was compiled with a
+particular feature enabled. See :attr:`~__future__._Feature.compiler_flag`.
 
 Other bits in :attr:`~codeobject.co_flags` are reserved for internal use.
 
 .. index:: single: documentation string
 
 If a code object represents a function and has a docstring,
-the first item in :attr:`~codeobject.co_consts` is
+:data:`~inspect.CO_HAS_DOCSTRING` bit is set in :attr:`~codeobject.co_flags`
+and the first item in :attr:`~codeobject.co_consts` is
 the docstring of the function.
 
 Methods on code objects