doc: add plugin section to admin section (template)

- Plugins configured at built time (defaults)
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/admin/index.rst

@@ -11,3 +11,4 @@ Administrator documentation
    filtron
    morty
    engines
+   plugins

docs/admin/plugins.rst

+.. _plugins generic:
+
+===============
+Plugins builtin
+===============
+
+.. sidebar:: Further reading ..
+
+   - :ref:`dev plugin`
+
+Configuration defaults (at built time):
+
+:DO: Default on
+
+.. _configured plugins:
+
+.. jinja:: webapp
+
+   .. flat-table:: Plugins configured at built time (defaults)
+      :header-rows: 1
+      :stub-columns: 1
+      :widths: 3 1 9
+
+      * - Name
+        - DO
+        - Description
+
+          JS & CSS dependencies
+
+      {% for plgin in plugins %}
+
+      * - {{plgin.name}}
+        - {{(plgin.default_on and "y") or ""}}
+        - {{plgin.description}}
+
+          {% for dep in (plgin.js_dependencies + plgin.css_dependencies) %}
+          | ``{{dep}}`` {% endfor %}
+
+      {% endfor %}

docs/dev/plugins.rst

+.. _dev plugin:
+
 =======
 Plugins
 =======
 
+.. sidebar:: Further reading ..
+
+   - :ref:`plugins generic`
+
 Plugins can extend or replace functionality of various components of searx.
 
 Example plugin