[mod] engines - add superuser.com (Stack Exchange API)

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

searx/settings.yml

@@ -1136,6 +1136,12 @@ engines:
     api_site: 'askubuntu'
     categories: it
 
+  - name: superuser
+    engine: stackexchange
+    shortcut: su
+    api_site: 'superuser'
+    categories: it
+
   - name: searchcode code
     engine: searchcode_code
     shortcut: scc