Help: Add notes for topic 'timestamp-names'

Help/release/dev/timestamp-names.rst

@@ -0,0 +1,6 @@
+timestamp-names
+---------------
+
+* The :command:`string(TIMESTAMP)` and :command:`file(TIMESTAMP)`
+  commands gained support for the ``%a`` and ``%b`` placeholders.
+  These are the abbreviated weekday and month names.