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 +28,75 @@ 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 created under ``/etc/apt/sources.list.d/`` by commenting
+          out the ``deb`` line, while keeping the ``deb-src`` line. It should look similar to this:
+
+          .. code-block:: bash
+
+              #deb http://ppa.launchpad.net/nest-simulator/nest/ubuntu focal main
+              deb-src http://ppa.launchpad.net/nest-simulator/nest/ubuntu focal main
+
+
+       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.
+          In addition, install:
+
+          ..  code-block:: bash
+
+              sudo apt install python3-all dh-python
+
+       5. After installing the dependencies, enter ``sudo apt source --build nest`` again.
+          When the build finished, look for lines like
+
+          ..  code-block:: bash
+
+              dpkg-deb: building package 'nest-dbgsym' in '../nest-dbgsym_2.20.0-0~202001311135~ubuntu20.04.1_amd64.deb'.
+              dpkg-deb: building package 'nest' in '../nest_2.20.0-0~202001311135~ubuntu20.04.1_amd64.deb'.
+              #dh binary
+              dpkg-genbuildinfo --build=binary
+              dpkg-genchanges --build=binary >../nest_2.20.0-0~202001311135~ubuntu20.04.1_amd64.changes
+
+          and note down the full package name. In the above example this would be
+          `nest_2.20.0-0~202001311135~ubuntu20.04.1_amd64.deb`, where the number `202001311135` and potentially the
+          Ubuntu version number may be different.
+
+       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
+
+          The package name is taken from the result of the previous step. `NUMBER` and potentially the Ubuntu
+          version might differ.
+
+       7. Test the package:
+
+          .. code-block:: bash
+
+             python3
+             import nest
+
+
    .. tab:: NeuroFedora
 
        The NeuroFedora team has generously provided the latest
@@ -51,7 +120,7 @@ compile NEST from source, see section** :ref:`advanced_install`.
 
           .. pull-quote::
 
-	     We strongly recommend that you **install all programs**
+          We strongly recommend that you **install all programs**
              you'll need, (such as ``ipython`` or ``jupyter-lab``) in
              the environment (ENVNAME) **at the same time**, by
              **appending them to the command below**.
@@ -265,5 +334,3 @@ these instructions.**
 
     Installation instructions for NEST 2.10 and earlier are provided :doc:`here <oldvers_install>`, but  we strongly encourage all our users to stay
     up-to-date with most recent version of NEST. We cannot support out-dated versions.
-
-