[docs] indicate modification of settings.yml is necessary to add new … (#6685)

* [docs] indicate modification of settings.yml is necessary to add new plugin + small exemple code correction
* [docs] plugins: add more details about adding new plugins

searx/plugins/__init__.py

@@ -27,10 +27,12 @@ Add Answer example
 Here is an example of a very simple plugin that adds a "Hello World" into the
 answer area:
 
+In ``searx/plugins`` create a file named ``hello_world.py`` with the following content:
+
 .. code:: python
 
    from flask_babel import gettext as _
-   from searx.plugins import Plugin
+   from searx.plugins import Plugin, PluginInfo
    from searx.result_types import Answer
 
    class MyPlugin(Plugin):
@@ -44,6 +46,23 @@ answer area:
        def post_search(self, request, search):
            return [ Answer(answer="Hello World") ]
 
+You will then need to add your new plugin in the :ref:`settings.yml` file like this:
+
+.. code:: yaml
+
+   plugins:
+     ...
+     searx.plugins.hello_world.MyPlugin:
+        active: true
+
+
+``searx.plugins.hello_world.MyPlugin`` is the Python import path of the new plugin we created.
+``searx.plugins.hello_world`` represents the file path, while ``MyPlugin`` represents the name of the plugin class.
+
+If you don't want the plugin to be part of SearXNG's core (i.e. maintain it independently of SearXNG),
+you may also place the file at any other path as long as you update the reference to it in :ref:`settings.yml`.
+For more examples, see :ref:`settings external_plugins`.
+
 .. _filter urls example:
 
 Filter URLs example