[docs] add documentation from the sources of the google engines

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

searx/settings.yml

@@ -583,6 +583,7 @@ engines:
   - name: google
     engine: google
     shortcut: go
+    # see https://searxng.github.io/searxng/src/searx.engines.google.html#module-searx.engines.google
     use_mobile_ui: true
     # additional_tests:
     #   android: *test_android