Add site setting site_description. If filled, it will be used in meta description tag for teh white hat SEO

app/controllers/categories_controller.rb

@@ -7,6 +7,8 @@ class CategoriesController < ApplicationController
   skip_before_filter :check_xhr, only: [:index]
 
   def index
+    @description = SiteSetting.site_description
+
     @list = CategoryList.new(guardian)
 
     @list.draft_key = Draft::NEW_TOPIC

app/controllers/list_controller.rb

@@ -11,6 +11,7 @@ class ListController < ApplicationController
       user = list_target_user
       list = TopicQuery.new(user, list_opts).public_send("list_#{filter}")
       list.more_topics_url = url_for(self.public_send "#{filter}_path".to_sym, list_opts.merge(format: 'json', page: next_page))
+      @description = SiteSetting.site_description if [:latest, :hot].include?(filter)
 
       respond(list)
     end

app/models/site_setting.rb

@@ -8,6 +8,7 @@ class SiteSetting < ActiveRecord::Base
 
   # settings available in javascript under Discourse.SiteSettings
   client_setting(:title, "Discourse")
+  setting(:site_description, '')
   client_setting(:logo_url, '/assets/d-logo-sketch.png')
   client_setting(:logo_small_url, '/assets/d-logo-sketch-small.png')
   setting(:contact_email, '')

config/locales/server.en.yml

@@ -459,6 +459,7 @@ en:
     discourse_org_access_key: "The access key used to access the Discourse Hub nickname registry at discourse.org"
     educate_until_posts: "Show pop-up composer education panel until the user has made this many posts"
     title: "Title of this site, will be used in the title tag and elsewhere"
+    site_description: "Describe this forum in one sentence. This description will be used in the meta description tag."
     contact_email: "The email address of someone who can be contacted about the site. Important notices from Discourse.org regarding critical updates may be sent to this address."
     company_full_name: "The full name of the company that runs this site, used in legal documents like the /tos"
     company_short_name: "The short name of the company that runs this site, used in legal documents like the /tos"