Add site setting show_create_topics_notice as a way to hide the 'Create at least 5 topics to get discussion started' message.

app/assets/javascripts/discourse.js

@@ -164,7 +164,7 @@ window.Discourse = Ember.Application.createWithMixins(Discourse.Ajax, {
       notices.push(I18n.t("read_only_mode.enabled"));
     }
 
-    if(Discourse.User.currentProp('admin')) {
+    if(Discourse.User.currentProp('admin') && Discourse.SiteSettings.show_create_topics_notice) {
       var topic_count = _.reduce(Discourse.Site.currentProp('categories'), function(sum,c) {
         return sum + (c.get('read_restricted') ? 0 : c.get('topic_count'));
       }, 0);

config/locales/server.en.yml

@@ -904,6 +904,7 @@ en:
     tos_accept_required: "If enabled, users will need to check a box on the signup form to confirm that they accept the terms of service. Edit 'Signup Form: Terms of Service Message' in the Content tab to change the message."
     notify_about_flags_after: "If there are flags that haven't been handled after this many hours, send an email to the contact_email. Set to 0 to disable."
     enable_cdn_js_debugging: "Allow /logs to display proper errors by adding crossorigin permissions on all js includes"
+    show_create_topics_notice: "If the site has fewer than 5 public topics, show a notice asking admins to create some topics."
 
   notification_types:
     mentioned: "%{display_username} mentioned you in %{link}"

config/site_settings.yml

@@ -547,3 +547,7 @@ uncategorized:
     default: ''
 
   enable_cdn_js_debugging: true
+  show_create_topics_notice:
+    client: true
+    default: true
+