[enh] add free software directory engine

searx/settings.yml

 # Or you can use the html non-stable engine, activated by default
     engine : flickr_noapi
 
+  - name : free software directory
+    engine : mediawiki
+    shortcut : fsd
+    categories : it
+    base_url : https://directory.fsf.org/
+    number_of_results : 5
+    search_type : title
+    timeout : 5.0
+    disabled : True
+
   - name : frinkiac
     engine : frinkiac
     shortcut : frk