Add NixOS install instructions

Author: fabaff

README.rst

@@ -20,6 +20,13 @@ On a Fedora-based system or on a CentOS/RHEL machine with has EPEL enabled.
 
     $ sudo dnf -y install python3-luftdaten
 
+For Nix or NixOS is `pre-packed module <https://search.nixos.org/packages?channel=unstable&from=0&size=50&sort=relevance&query=luftdaten>`_
+available. The lastest release is usually present in the ``unstable`` channel.
+
+.. code:: bash
+
+    $nix-env -iA nixos.python39Packages.luftdaten
+
 Usage
 -----