Add description for the age and confirm_lag fields

Author: xuniq

doc/reference/reference_lua/box_info/synchro.rst

@@ -1,8 +1,7 @@
 ..  _box_info_synchro:
 
-================================================================================
 box.info.synchro
-================================================================================
+================
 
 ..  module:: box.info
 
@@ -42,6 +41,11 @@ box.info.synchro
             (for example, ``PROMOTE``, ``CONFIRM``, or ``ROLLBACK``).
             Until the request is complete, any other incoming synchronous transactions and system requests
             will be delayed.
+        -   ``age`` (since version :doc:`3.2.0 </release/3.2.0>`) -- the time in seconds that the oldest entry currently
+            present in the queue has spent waiting for the quorum to collect.
+
+        -   ``confirm_lag`` (since version :doc:`3.2.0 </release/3.2.0>`) -- the time in seconds that the latest successfully
+            confirmed entry waited for the quorum to collect.
 
     *   ``quorum`` -- the resulting value of the
         :ref:`replication_synchro_quorum <cfg_replication-replication_synchro_quorum>` configuration option.