Add a todo note in docs

Author: XuehaiPan

Doc/library/sys.rst

@@ -35,6 +35,11 @@ always available. Unless explicitly noted otherwise, all variables are read-only
       <whatsnew314-sys-abiflags-change>` on the *What's New in 3.14*
       page for more details.
 
+   .. TODO: When we're in Python 3.16:
+      - Add a **CAUTION** section about the differences of :data:`sys.abiflags`
+        between prior-3.14, 3.14-3.15, and 3.16+ on Windows.
+      - Move porting recommendations from whatsnew/3.14.rst.
+
 
 .. function:: addaudithook(hook)
 

Doc/whatsnew/3.14.rst

@@ -960,7 +960,7 @@ To suppress this warning, use the :mod:`warnings` module:
    import warnings
 
    with warnings.catch_warnings():
-       # ignore DeprecationWarning on sys.abiflags change on Windows
+       # ignore DeprecationWarning on incoming sys.abiflags change on Windows before 3.16
        warnings.simplefilter('ignore', DeprecationWarning)
        abiflags = getattr(sys, 'abiflags', '')