Add description as comment on topic.

db/migrate/20170807082243_create_topics.rb

@@ -2,6 +2,7 @@ class CreateTopics < ActiveRecord::Migration
   def change
     create_table :topics do |t|
       t.string :title, null: false
+      t.text   :description_as_comment
       t.integer :author_id
       t.integer  "comments_count", default: 0
       t.references :community, index: true

db/schema.rb

@@ -891,13 +891,14 @@ ActiveRecord::Schema.define(version: 20170807082243) do
   add_index "tags", ["spending_proposals_count"], name: "index_tags_on_spending_proposals_count", using: :btree
 
   create_table "topics", force: :cascade do |t|
-    t.string   "title",                      null: false
+    t.string   "title",                              null: false
+    t.text     "description_as_comment"
     t.integer  "author_id"
-    t.integer  "comments_count", default: 0
+    t.integer  "comments_count",         default: 0
     t.integer  "community_id"
     t.datetime "hidden_at"
-    t.datetime "created_at",                 null: false
-    t.datetime "updated_at",                 null: false
+    t.datetime "created_at",                         null: false
+    t.datetime "updated_at",                         null: false
   end
 
   add_index "topics", ["community_id"], name: "index_topics_on_community_id", using: :btree