[mod] enable autocomplete from duckduckgo by default

Closes: https://github.com/searxng/searxng/issues/1889
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings.yml

@@ -26,7 +26,7 @@ search:
   # Existing autocomplete backends: "dbpedia", "duckduckgo", "google", "yandex",
   # "seznam", "startpage", "swisscows", "qwant", "wikipedia" - leave blank to turn it off
   # by default.
-  autocomplete: ""
+  autocomplete: "duckduckgo"
   # minimun characters to type before autocompleter starts
   autocomplete_min: 4
   # Default search language - leave blank to detect from browser information or