Mention that the allow-transfer option has been extended

This commit updates both the reference manual and release notes with
the information that 'allow-transfer' has been extended with
additional "port" and "transport" options.

doc/notes/notes-current.rst

@@ -35,7 +35,13 @@ Removed Features
 Feature Changes
 ~~~~~~~~~~~~~~~
 
-- None.
+- The ``allow-transfers`` option was extended to accept additional
+  ``port`` and ``transport`` parameters, to further restrict zone
+  transfers to a particular port and DNS transport protocol. Either of
+  these options can be specified.
+
+  For example: ``allow-transfer port 853 transport tls { any; };``
+  :gl:`#2776`
 
 Bug Fixes
 ~~~~~~~~~