Update Debian installation instructions

doc/installation/index.rst

@@ -11,9 +11,9 @@ compile NEST from source, see section** :ref:`advanced_install`.
 .. tabs::
 
 
-   .. tab:: Debian/Ubuntu PPA
+   .. tab:: Ubuntu
 
-       Install NEST via the PPA repository.
+       Ubuntu users can install NEST via the PPA repository.
 
        1. Add the PPA repository for NEST and update apt:
 
@@ -28,6 +28,47 @@ compile NEST from source, see section** :ref:`advanced_install`.
 
            sudo apt-get install nest
 
+
+   .. tab:: Debian
+
+       Debian users can install NEST via the Ubuntu PPA repository.
+
+       1. Create a new ``apt`` repository entry in ``/etc/apt/sources.list.d/nest-simulator-ubuntu-nest-XXX.list`` by:
+
+       .. code-block:: bash
+
+          sudo apt install devscripts build-essential software-properties-common dpkg-dev
+          sudo add-apt-repository --enable-source ppa:nest-simulator/nest
+
+       2. Disable the binary package in the repository file by commenting it out.
+
+       3. Import the PPA GPC key and rebuild the package:
+
+       .. code-block:: bash
+
+          sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 \
+                           --recv-keys 0CF7539642ABD23CBCA8D487F0B8B6C5EC02D7DD
+          sudo apt update
+          sudo apt source --build nest
+
+       4. Install any missing dependencies, if ``apt`` tells you so.
+
+       5. After installing the dependencies, enter ``sudo apt source --build nest`` again.
+
+       6. Install the ready Debian package after the rebuild:
+
+       ..  code-block:: bash
+
+           sudo dpkg --install nest-simulator-x.y.z~NUMBER~ubuntu20.04.1_amd64.deb
+
+       7. Test the package:
+
+       .. code-block:: bash
+
+          python3
+          import nest
+
+
    .. tab:: NeuroFedora
 
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