doc: moved reST sources in the right folder (much clearer)

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

docs/index.rst

@@ -1,3 +1,4 @@
+================
 Welcome to searx
 ================
 
@@ -22,37 +23,10 @@ searx can be used over Tor for online anonymity.
 Get started with searx by using one of the :wiki:`Searx-instances`.  If you
 don't trust anyone, you can set up your own, see :ref:`installation`.
 
-
-User documentation
-------------------
-
 .. toctree::
-   :maxdepth: 1
+   :maxdepth: 2
 
-   user/search_syntax
-   user/own-instance
-
-Administrator documentation
----------------------------
-
-.. toctree::
-   :maxdepth: 1
-
-   dev/install/installation
-   admin/api
-   admin/filtron
-   admin/morty
-   blog/blog
-
-Developer documentation
------------------------
-
-.. toctree::
-   :maxdepth: 1
-
-   dev/quickstart
-   dev/contribution_guide
-   dev/engine_overview
-   dev/search_api
-   dev/plugins
-   dev/translation
+   user/index
+   admin/index
+   dev/index
+   blog/index