Improve enabling command expansion section (neo4j#2470)

Author: renetapopova

modules/ROOT/pages/configuration/command-expansion.adoc

@@ -41,14 +41,31 @@ Scripts and their syntax differ between operating systems.
 
 == Enabling
 
-The Neo4j startup script and the `neo4j` service can expand and execute the external commands by using the argument `--expand-commands`.
+To enable command expansion, you must add the `--expand-commands` argument to the Neo4j startup script or _neo4j.service_ file.
+
+=== Starting Neo4j with command expansion
+
+To start Neo4j with command expansion enabled, you can use the following command:
 
 [source, shell]
 ----
 bin/neo4j start --expand-commands
 ----
 
-If the startup script does not receive the `--expand-commands` argument, commands in the configuration file are treated as invalid settings.
+=== Enabling command expansion in Neo4j as a service
+
+If you are using Neo4j as a service, you can enable command expansion by adding the `--expand-commands` argument to the _/etc/systemd/system/neo4j.service_  file.
+Otherwise, the commands in the configuration file are treated as invalid settings.
+
+You must also add `Type=forking` under the `[Service]` section of _/etc/systemd/system/neo4j.service_ to allow for the command expansion.
+
+[source]
+----
+[Service]
+Type=forking
+----
+
+=== Security checks
 
 Neo4j performs the following basic security checks on the _neo4j.conf_ file.
 If they fail, Neo4j does not evaluate the script commands in _neo4j.conf_, and the Neo4j process does not start.