Update create instructions for installing on existing VM

docs/installation_instructions.md

@@ -191,16 +191,15 @@ its *hostname* and its *IP address*. Also check that your VPS meets our
 > properly so please don't use this option by default.
 
 If you want your cluster to be reachable under the fully qualified domain name
-(`FQDN`) `my-cluster.oas.example.org`, the corresponding parameters would be:
+(`FQDN`) `oas.example.org`, the corresponding parameters would be:
 
-* `--hostname`: `my-cluster`
 * `--subdomain`: `oas`
-* the `DOMAIN`: `example.org`
+* your `DOMAIN`: `example.org`
 
 Create the OpenAppStack settings for your VPS by running the following command:
 
 ```
-$ python -m openappstack my-cluster create --ip-address IP_ADDRESS --hostname HOSTNAME --subdomain oas example.org
+$ python -m openappstack my-cluster create --ip-address IP_ADDRESS --subdomain oas example.org
 ```
 
 ### DNS entries