add link in README to discussion on emoji domains

Author: JoshData

README.rst

@@ -132,16 +132,18 @@ Internationalized domain names (IDN)
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 The first is `internationalized domain names (RFC
-5891) <https://tools.ietf.org/html/rfc5891>`__. The DNS system has not
+5891) <https://tools.ietf.org/html/rfc5891>`__, a.k.a IDNA 2008. The DNS system has not
 been updated with Unicode support. Instead, internationalized domain
 names are converted into a special IDNA ASCII form starting with
 ``xn--``. When an email address has non-ASCII characters in its domain
 part, the domain part is replaced with its IDNA ASCII equivalent form
 in the process of mail transmission. Your mail submission library probably
 does this for you transparently. Note that most web browsers are currently
-in transition between IDNA 2003 (RFC 3490) and IDNA 2008 (RFC 5891). This
-library uses IDNA 2008 using the `idna <https://github.com/kjd/idna>`__
-module by Kim Davies.
+in transition between IDNA 2003 (RFC 3490) and IDNA 2008 (RFC 5891) and
+[compliance around the web is not very good](http://archives.miloush.net/michkap/archive/2012/02/27/10273315.html)
+in any case, so be aware that edge cases are handled differently by different
+applications and libraries. This library conforms to IDNA 2008 using the
+`idna <https://github.com/kjd/idna>`__ module by Kim Davies.
 
 Internationalized local parts
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