Docs: more explanation of the implications of new tail-call interpreter (GH-129863)

Co-authored-by: Ken Jin <[email protected]>

Author: nedbat

Doc/whatsnew/3.14.rst

@@ -235,9 +235,13 @@ For further information on how to build Python, see
    This is not to be confused with `tail call optimization`__ of Python
    functions, which is currently not implemented in CPython.
 
+   This new interpreter type is an internal implementation detail of the CPython
+   interpreter.  It doesn't change the visible behavior of Python programs at
+   all.  It can improve their performance, but doesn't change anything else.
+
    __ https://en.wikipedia.org/wiki/Tail_call
 
-(Contributed by Ken Jin in :gh:`128718`, with ideas on how to implement this
+(Contributed by Ken Jin in :gh:`128563`, with ideas on how to implement this
 in CPython by Mark Shannon, Garrett Gu, Haoran Xu, and Josh Haberman.)