[docs] move article "XPath Engine" to to admin/engines/

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

docs/admin/engines.rst

@@ -16,6 +16,7 @@ Special Engine Settings
    engines/recoll
    engines/sql-engines
    engines/command-line-engines
+   engines/searx.engines.xpath
 
 
 .. _engines generic:

docs/admin/engines/searx.engines.xpath.rst

@@ -0,0 +1,9 @@
+.. _xpath engine:
+
+============
+XPath Engine
+============
+
+.. automodule:: searx.engines.xpath
+  :members:
+

docs/src/searx.engines.xpath.rst

@@ -1,9 +0,0 @@
-.. _xpath_engine:
-
-================
-The XPath engine
-================
-
-.. automodule:: searx.engines.xpath
-  :members:
-