Fix twitter config description

It's not optional

client/src/app/+admin/config/edit-custom-config/edit-custom-config.component.html

@@ -651,7 +651,8 @@
           <div class="form-group col-12 col-lg-4 col-xl-3">
             <div i18n class="inner-form-title">TWITTER</div>
             <div i18n class="inner-form-description">
-              Optional. If any, provide the Twitter account representing your instance to improve link previews.
+              Provide the Twitter account representing your instance to improve link previews.
+              If you don't have a Twitter account, just leave the default value.
             </div>
           </div>