Update docs and changelog for URI, RFC822Name, and DNSName (#3955)

* Update docs and changelog for URI, RFC822Name, and DNSName

As of 2.1 we want users to pass A-label strings, but we still accept
U-label strings and auto-encode on their behalf (with a deprecation
warning). However, we do not return U-label in the value attribute so
we are making a backwards incompatible change for users that utilize
internationalized domain names.

* language updates

* add presentational to the word list

* the linux dictionary is pathetic
diff --git a/docs/glossary.rst b/docs/glossary.rst
index df32760..ce08dba 100644
--- a/docs/glossary.rst
+++ b/docs/glossary.rst
@@ -94,5 +94,10 @@
         bit key, you can calculate the number of bytes by dividing by 8. 128
         divided by 8 is 16, so a 128 bit key is a 16 byte key.
 
+    U-label
+        The presentational unicode form of an internationalized domain
+        name. U-labels use unicode characters outside the ASCII range and
+        are encoded as A-labels when stored in certificates.
+
 .. _`hardware security module`: https://en.wikipedia.org/wiki/Hardware_security_module
 .. _`idna`: https://pypi.org/project/idna/