add item set with scaffold

db/migrate/20170811071000_create_item_sets.rb

@@ -0,0 +1,11 @@
+class CreateItemSets < ActiveRecord::Migration[5.1]
+  def change
+    create_table :item_sets do |t|
+      t.string :name
+      t.integer :min_selectable_qty
+      t.integer :max_selectable_qty
+
+      t.timestamps
+    end
+  end
+end