Fix link text in start_stop_instance.rst (#3745)

Author: p7nov

doc/book/admin/start_stop_instance.rst

@@ -27,7 +27,7 @@ If there are several enabled instances, ``tt start`` starts a separate Tarantool
 instance for each of them.
 
 Learn more about working with multiple Tarantool instances in
-:ref:`Managing multiple instances <admin-start_stop_instance-multi-instance>`.
+:ref:`Multi-instance applications <admin-start_stop_instance-multi-instance>`.
 
 To start a specific enabled instance, specify its name in the ``tt start`` argument:
 
@@ -332,4 +332,4 @@ To restart a running ``my_app`` instance with ``systemctl``, run:
 
 .. code-block:: console
 
-    $ systemctl restart tarantool@my_app
+    $ systemctl restart tarantool@my_app