add more tooltips to preferences

searx/templates/oscar/preferences.html

                             {% endfor %}
                         </select>
                     </div>
+                    <span class="col-sm-5 col-md-6 help-block">{{ _('What language do you prefer for search?') }}</span>
                 </div>
                 
                 
                             {% endfor %}
                         </select>
                     </div>
+                    <span class="col-sm-5 col-md-6 help-block">{{ _('Change the language of the layout') }}</span>
                 </div>
                 <div class="row form-group">
                     <label class="col-sm-3 col-md-2">{{ _('Autocomplete') }}</label>