gh-137113 docs: note readline no longer supported in REPL after 3.13

Doc/library/readline.rst

@@ -7,6 +7,10 @@
 
 .. sectionauthor:: Skip Montanaro <skip.montanaro@gmail.com>
 
+.. note::
+   The new :term:`REPL` introduced in version 3.13 doesn't support readline.
+   However, readline can still be used by setting the :envvar:`PYTHON_BASIC_REPL` environment variable.
+
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 The :mod:`readline` module defines a number of functions to facilitate