[doc] update documentation of the installation procedures

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/utils/searxng.sh.rst

@@ -0,0 +1,36 @@
+
+.. _searxng.sh:
+
+====================
+``utils/searxng.sh``
+====================
+
+.. sidebar:: further reading
+
+   - :ref:`architecture`
+   - :ref:`installation`
+   - :ref:`installation nginx`
+   - :ref:`installation apache`
+
+To simplify installation and maintenance of a SearXNG instance you can use the
+script :origin:`utils/searxng.sh`.
+
+Install
+=======
+
+In most cases you will install SearXNG simply by running the command:
+
+.. code::  bash
+
+   sudo -H ./utils/searx.sh install all
+
+The installation is described in chapter :ref:`installation basic`.
+
+.. _searxng.sh overview:
+
+Overview
+========
+
+The ``--help`` output of the script is largely self-explanatory:
+
+.. program-output:: ../utils/searxng.sh --help