gh-137113 docs: note readline no longer supported in REPL after 3.13 (GH-137142)

Add a note to the readline module documentation stating that
Python 3.13 and later no longer supports readline in the default REPL,
as per gh-118840. Includes workaround using PYTHON_BASIC_REPL.

Update tutorial to remove the reference, and use a different key to
test things out.

Signed-off-by: Kuang Yu Heng <yuheng3107@gmail.com>