Document class mappings in changelog

Signed-off-by: martin f. krafft <madduck@madduck.net>
diff --git a/doc/source/changelog.rst b/doc/source/changelog.rst
index a5b95e4..14b7583 100644
--- a/doc/source/changelog.rst
+++ b/doc/source/changelog.rst
@@ -5,6 +5,8 @@
 ========= ========== ========================================================
 Version   Date       Changes
 ========= ========== ========================================================
+                     * Introduce class mappings (see :doc:`operations`)
+                       (closes: #5)
                      * Fix parameter interpolation across merged lists
                        (closes: #13).
                      * Caching of classes for performance reasons, especially