[doc] rearranges Settings & Engines docs for better readability

We have built up detailed documentation of the *settings* and the *engines* over
the past few years.  However, this documentation was still spread over various
chapters and was difficult to navigate in its entirety.

This patch rearranges the Settings & Engines documentation for better
readability.

To review new ordered docs::

   make docs.clean docs.live

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

searx/engines/recoll.py

@@ -1,6 +1,51 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
-"""
- Recoll (local search engine)
+# lint: pylint
+""".. sidebar:: info
+
+   - `Recoll <https://www.lesbonscomptes.com/recoll/>`_
+   - `recoll-webui <https://framagit.org/medoc92/recollwebui.git>`_
+   - :origin:`searx/engines/recoll.py`
+
+Recoll_ is a desktop full-text search tool based on Xapian.  By itself Recoll_
+does not offer WEB or API access, this can be achieved using recoll-webui_
+
+Configuration
+=============
+
+You must configure the following settings:
+
+``base_url``:
+  Location where recoll-webui can be reached.
+
+``mount_prefix``:
+  Location where the file hierarchy is mounted on your *local* filesystem.
+
+``dl_prefix``:
+  Location where the file hierarchy as indexed by recoll can be reached.
+
+``search_dir``:
+  Part of the indexed file hierarchy to be search, if empty the full domain is
+  searched.
+
+Example
+=======
+
+Scenario:
+
+#. Recoll indexes a local filesystem mounted in ``/export/documents/reference``,
+#. the Recoll search interface can be reached at https://recoll.example.org/ and
+#. the contents of this filesystem can be reached though https://download.example.org/reference
+
+.. code:: yaml
+
+   base_url: https://recoll.example.org/
+   mount_prefix: /export/documents
+   dl_prefix: https://download.example.org
+   search_dir: ''
+
+Implementations
+===============
+
 """
 
 from datetime import date, timedelta
@@ -33,7 +78,7 @@ embedded_url = '<{ttype} controls height="166px" ' + 'src="{url}" type="{mtype}"
 
 # helper functions
 def get_time_range(time_range):
-    sw = {'day': 1, 'week': 7, 'month': 30, 'year': 365}
+    sw = {'day': 1, 'week': 7, 'month': 30, 'year': 365}  # pylint: disable=invalid-name
 
     offset = sw.get(time_range, 0)
     if not offset: