Add some hints how OMV behaves.

Fixes: openmediavault/openmediavault#1381
Signed-off-by: Volker Theile <votdev@gmx.de>

installation/index.rst

@@ -18,7 +18,7 @@ Installation variants:
 
 	* :doc:`Dedicated drive </installation/via_iso>` - Advised method via ISO image. This runs OMV from its own drive.
 	* :doc:`USB flash drive </installation/on_usb>` - This runs |omv| from a USB flash drive.
-	* :doc:`Debian Operating System </installation/on_debian>` - This runs |omv| as a services on top of a Debian OS.
+	* :doc:`Debian Operating System </installation/on_debian>` - Use an existing Debian OS installation for |omv|.
 	* `Debian Operating System via debootstrap <https://forum.openmediavault.org/index.php/Thread/12070-GUIDE-DEBOOTSTRAP-Installing-Debian-into-a-folder-in-a-running-system/>`_. Use this as a last resort in case the installer does not recognize a specific essential hardware component like hard disk (NVME) or a network card that needs a higher kernel (backport).
 	* :doc:`SD card </installation/via_image>` - This runs |omv| from a SD card.
 
@@ -34,8 +34,8 @@ First time use:
 .. note::
    |omv| will enable SSH access for the user ``root`` by default to be
    able to access a headless system in case of a broken installation or
-   other maintenance situations. You can disable this behaviour in the
-   ``Services | SSH`` page.
+   other maintenance situations. You should disable this behaviour in the
+   ``Services | SSH`` page for security reasons after installation.
 
    To still get ``root`` access you need to create a non-privileged user
    and add them to the ``ssh`` and ``sudo`` groups. After that you can

installation/on_debian.rst

@@ -1,18 +1,24 @@
 Installation on Debian
 ######################
 
-You can install |omv| on a Debian installation as well.
+You can install |omv| on an existing Debian installation as well.
 
-To do so, on x86 simply install the system using the `Debian netinst images
+.. note::
+   The installation of |omv| will be denied if a graphical desktop environment is detected.
+
+.. note::
+    |omv| does not import any existing settings of your system, except for network and time related settings.
+
+To do so, simply install the system using the `Debian netinst images
 <https://www.debian.org/CD/netinst/>`_. After that apply the commands below.
-Please do **not** install a graphical environment, use a minimal server
+Please do **not** install a graphical desktop environment, use a minimal server
 installation only. For a step by step install guide have a look into the
 `Debian minimal install guide <https://www.pcsuggest.com/debian-minimal-install-guide/>`_.
 
-On ARM devices check if there's an appropriate `Armbian <https://www.armbian.com/download>`_
-Buster (Debian 10) image available. After installing Armbian then use the
+On ARM devices, please check if there's an appropriate `Armbian <https://www.armbian.com/download>`_
+image available. After installing Armbian, then use the
 `armbian-config` tool to install OMV in a single step with all performance and reliability
-tweaks included. If there's no Armbian for your device simply follow the steps outlined
+tweaks included. If there's no Armbian image for your device, simply follow the steps outlined
 below.
 
 On `Raspberry Pi OS <https://www.raspberrypi.org/software/operating-systems/>`_ the below