bpo-44964: Add a note explaining the new semantics of f_last_i in frame objects (GH-28200)

(cherry picked from commit fa2c0b85a8d5c9486661083afdf38cbaadb3432a)

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index eefdc3d..477daae 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -1034,8 +1034,9 @@
       :attr:`f_code` is the code object being executed in this frame; :attr:`f_locals`
       is the dictionary used to look up local variables; :attr:`f_globals` is used for
       global variables; :attr:`f_builtins` is used for built-in (intrinsic) names;
-      :attr:`f_lasti` gives the precise instruction (this is an index into the
-      bytecode string of the code object).
+      :attr:`f_lasti` gives the precise instruction (it represents a wordcode index, which
+      means that to get an index into the bytecode string of the code object it needs to be
+      multiplied by 2).
 
       Accessing ``f_code`` raises an :ref:`auditing event <auditing>`
       ``object.__getattr__`` with arguments ``obj`` and ``"f_code"``.