Fix gh-893 feedback: Submodule box.info

Added follow status.
Will need a translation.

Author: Vladimir I

doc/book/box/box_info.rst

@@ -182,9 +182,12 @@ variables.
       Even if an instance is :ref:`removed <replication-remove_instances>`,
       its values will still appear here.
 
-    * **replication.downstream.status** ``= disconnected`` is displayed if the
-      downstream instance disconnects from the upstream instance. Otherwise the
-      status is not reported.
+    * **replication.downstream.status** is the replication status for downstream
+      replications:
+
+      * ``disconnected`` is displayed if the downstream instance disconnects
+        from the upstream instance.
+      * ``follow`` means that downstream replication is in progress.
 
 .. function:: box.info()