bpo-17305: Link to the third-party idna package. (GH-25208)

So long as we don't have idna2008 in the standard library, we should at least point people to the third-party solution.
(cherry picked from commit 1d023e374cf96d143b065242131ddc9b889f9a1e)

Co-authored-by: Gregory P. Smith <greg@krypto.org>

diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index 6eb907afce3c6c30f05f2b7d7113d9b0e82df3cc..32fbc831ca2c8793b18df759fdc342a0a392eaea 100644 (file)
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -1414,6 +1414,9 @@ Applications) and :rfc:`3492` (Nameprep: A Stringprep Profile for
 Internationalized Domain Names (IDN)). It builds upon the ``punycode`` encoding
 and :mod:`stringprep`.
 
+If you need the IDNA 2008 standard from :rfc:`5891` and :rfc:`5895`, use the
+third-party `idna module <https://pypi.org/project/idna/>_`.
+
 These RFCs together define a protocol to support non-ASCII characters in domain
 names. A domain name containing non-ASCII characters (such as
 ``www.Alliancefrançaise.nu``) is converted into an ASCII-compatible encoding