datetime: refined leap second support desc

Author: tmr-g

doc/reference/reference_lua/datetime.rst

@@ -118,7 +118,7 @@ Functions
                 -   0
 
             *   -   sec
-                -   Seconds. Value range: 0 - 60. A leap second is supported, see a section :ref:`leap second <leap-second>`.
+                -   Seconds. Value range: 0 - 60. A leap second is inchoately supported, see a section :ref:`leap second <leap-second>`.
                 -   number
                 -   0
 
@@ -267,7 +267,7 @@ Functions
 
     By default fields that are not specified are equal to appropriate values in a Unix time.
 
-    Leap second is supported, see a section :ref:`leap second <leap-second>`.
+    Leap second is inchoately supported, see a section :ref:`leap second <leap-second>`.
 
     :param string input_string: string with the date and time information.
     :param string format: indicator of the ``input_string`` format.
@@ -1098,7 +1098,8 @@ that besides the time zone description files also contains a leapseconds file.
 You can use the Lua module :ref:`tarantool <tarantool-module>` to get a used
 version of ``tzdata``.
 
-This section describes how the ``datetime`` module supports leap seconds:
+This section describes how the ``datetime`` module supports leap seconds.
+It's very initially level of support:
 
 *   The function :ref:`datetime.parse() <datetime-parse>` correctly parses
     an input string with 60 seconds: