add user model

db/migrate/20210804230323_create_users.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+class CreateUsers < ActiveRecord::Migration[6.1]
+  def change
+    create_table(:users) do |t|
+      t.string(:first_name, null: false)
+      t.string(:last_name, null: false)
+      t.string(:email, null: false)
+
+      t.timestamps
+    end
+
+    add_index(:users, :email, unique: true)
+  end
+end