add currency entity

db/migrate/20210811014107_create_currencies.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+class CreateCurrencies < ActiveRecord::Migration[6.1]
+  def change
+    create_table(:currencies) do |t|
+      t.string(:name, null: false)
+
+      t.timestamps
+    end
+  end
+end