[day-02] add user schema and migration

Add elixir struct to represent an user and its corresponding
representation on the database.

priv/repo/migrations/20210622015725_create_users_table.exs

@@ -0,0 +1,15 @@
+defmodule Wabanex.Repo.Migrations.CreateUsersTable do
+  use Ecto.Migration
+
+  def change do
+    create table(:users) do
+      add :email, :string
+      add :name, :string
+      add :password, :string
+
+      timestamps()
+    end
+
+    create unique_index(:users, [:email])
+  end
+end