add installation instructions with --ip-address and --hostname arguments

docs/installation_instructions.md

@@ -32,6 +32,7 @@ guide][https://openappstack.net/contact.html).
   * at least 20GB of disk space for installation, plus more for application
     data;
   * root ssh access.
+  * python installed
 * A trusted local machine to run the installer on:
   * You need Python 3 and Git installed (`apt install python3 git`)
   * We recommend using a [python virtualenv](https://docs.python.org/3/tutorial/venv.html)
@@ -173,8 +174,19 @@ There are two options to create a cluster:
 
 #### Any other VPS or bare metal server
 
-Sorry, this will be implemented ASAP! Track [this
-issue](https://open.greenhost.net/openappstack/openappstack/issues/317)
+If you want to follow this step, we assume you already have a VPS. You'll need
+its *hostname* and its *IP address*. Also check that your VPS meets our
+[prerequisites](#prerequisites). 
+
+> **WARNING:** the OpenAppStack installation makes substantial changes to your
+> whole VPS and needs root access. It is not advised to follow these
+> instructions on a VPS that you are using for something else too.
+
+Create the OpenAppStack settings for your VPS by running the following command: 
+
+```
+$ python -m openappstack create --ip-address IP_ADDRESS --hostname HOSTNAME
+```
 
 ### DNS entries