Update docs

docs/configuration.rst

@@ -62,7 +62,9 @@ there is a good way to disable rate limiting altogether.
 The ``TLS_FLAVOR`` sets how Mailu handles TLS connections. Setting this value to
 ``notls`` will cause Mailu not to server any web content! More on :ref:`tls_flavor`.
 
-The ``TZ`` sets the timezone Mailu will use. The timezone naming convention usually uses a ``Region/City`` format. This defaults to ``Etc/UTC``
+The ``TZ`` sets the timezone Mailu will use. The timezone naming convention usually uses a ``Region/City`` format. See `TZ database name`_  for a list of valid timezones This defaults to ``Etc/UTC``
+
+.. _`TZ database name`: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
 
 Mail settings
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